OED is describing an ugly use of the word "source" because it has accepted that it is in common currency. The examples you give are exactly what I mean.

Each type of coffee is/comes from one country. She was called upon to find a supply/supplier of carpeting.

What next? "He doored it" = He left by the door. "She windowed" = "She opened the window. Is "We railroaded it to Chicago" the same as "we went by train"? We automobiled it to Chicago. He treed his golf ball. Cleopatra was carpeted to Caesar.

Okay, so I was carpeted by the boss a few times, and it was nothing like Cleopatra's experience.

retired teacher

Shaune has my total agreement: it is refreshing to read that I am not alone in wanting to strike people who commit such atrocities upon the English language as to use "action" as a verb. For years I had a boss who had made his way to England from the colonies, who always wanted to "action" things, and "farewell" people. ( In my case he eventually did. ) Of course we all mocked him for these examples, but the one which gives me the greatest annoyance these days is used by so many people that I dare not laugh: people who go about "sourcing" things. Source is not a verb. It comes from "surgo" in Latin, to rise, and is not transitive. "Soudre" in French, too, is a verb, and it means to spring forth, also not transitive. You cannot source a thing. Source is a noun. "It sourced in Africa" sounds all wrong, because it is, (intransitive) but "I sourced it in Africa" (transitive) is even more horrible, I reckon. "Its source is in Africa" is an odd way of saying "It comes from Africa", but at least it is grammatical. But there is no need whatever to coin a new word for "find a supplier" or whatever these folk think they mean when they talk about "sourcing" things.
I thought all these grammatical and linguistic horrors came from American English, but I see from the comments throughout this site that I was wrong. The British seem not to care at all about what is happening to the English language; Americans do. Keep up the good work!!

Shaune has my total agreement: it is refreshing to read that I am not alone in wanting to strike people who commit such atrocities upon the English language as to use "action" as a verb. For years I had a boss who had made his way to England from the colonies, who always wanted to "action" things, and "farewell" people. ( In my case he eventually did. ) Of course we all mocked him for these examples, but the one which gives me the greatest annoyance these days is used by so many people that I dare not laugh: people who go about "sourcing" things. Source is not a verb. It comes from "surgo" in Latin, to rise, and is not transitive. "Soudre" in French, too, is a verb, and it means to spring forth, also not transitive. You cannot source a thing. Source is a noun. "It sourced in Africa" sounds all wrong, because it is, (intransitive) but "I sourced it in Africa" (transitive) is even more horrible, I reckon. "Its source is in Africa" is an odd way of saying "It comes from Africa", but at least it is grammatical. But there is no need whatever to coin a new word for "find a supplier" or whatever these folk think they mean when they talk about "sourcing" things.
I thought all these grammatical and linguistic horrors came from American English, but I see from the comments throughout this site that I was wrong. The British seem not to care at all about what is happening to the English language; Americans do. Keep up the good work!!

At the school in Scotland I attended as a youth, one large, 19th C set of gentlemen's facilities there was known officially as "The House of Lords". But this name was just for that particular place, not for use elsewhere. In Britain these days the term "toilet" is bandied about a great deal, but nearly always without the final "t": toile' with an ugly final glottal stop is the term employed by those Britons who favour this word, so pronounced "Toy-luh' (momentary silence while mouth remains hanging open and eyes continue to glaze over)".
'Lavatory' is preferred by the more refined. "Lavvy" is intended to be a humorous variant. 'Loo' is very ladylike, being a corruption of the French lieu="place". "Bog" is favoured by otherwise well-spoken schoolboys anxious to establish some street-cred. "Heads" is navy, "latrine" American.
You would think we would just call the by its proper name, would you not? The

"We will have a staff meeting tomorrow" is just as bad a thing to hear as "We will have a staff meeting on tomorrow". Firstly, it should be "We shall have ..." and secondly, who would want to go a staff meeting?

Shakespeare's Othello:
"Beware the green-ey'd monster, Jealousy". Shame about having green eyes, which you share with this monster, when you are not jealous too.

Brus

Valentina,
you hit the nail on the head. The politicians speak incorrect English even when they do know the difference, in order to seem demotic, and thereby not lose the votes of those who might think them acting as if superior if they were to get it right. Strange, is it not? Yes, I think this is peculiar to English. Something to do with the climate, perhaps.

Who wrote this nonsense in the American Heritage Book of English Usage you quote? It is made up as he goes along by the writer, I suggest. It is obvious that "if I was" is incorrect English, and is what we might call demotic, or an attempt by the speaker to seem demotic to avoid being accused of being elitist, that is, educated. Or a clumsy, unprepared and wholly excusable minor gaffe in casual speech in a casual situation. None of these is what one wants of a hopeful politician in a formal situation, I argue.

Valentina raises interesting questions. Is the preference for 'informal' speech in any way motivated by a desire to be 'American', or to avoid being accused of pedantry? Not American, I think: Frasier Crane and Niles get it right!
Mr Ed Miliband is a man of education and high office in Britain. Is his choice of slang "was" in place of 'correct' "were" in a hypothetical "If I were the prime minister..." motivated by a wish not to seem pedantic, perhaps? What is wrong with being correct? Why is it pedantic? I am sure we all know the reason for that!

If you prefer "This is her" instead, "her" is being used disjunctively, as in French "C'est moi", infinitely preferable to "C'est je". Okay?