Got it or Don't Got It?

A: Have you got it? B: No, I don't. A: What? You don't got it, you say? B: No, I don't. I first heard this many years ago from a Northern Irish friend and he seemed to see nothing unusual in the construction. Time has proved him right and me wrong, again. Nowadays most US speakers and possibly most UK under 40s would agree with him. They say NI accents were a big influence in the New World and maybe that's where this grammatical construction and more common use of "don't have" rather than "haven't got" comes from? I still miss the distinction, as in the old joke about the American doctor working in Britain: Dr: Now Mrs Smith how many children do you have? Mrs S:( looking worried) Oh, dear, normally only one at a time, doctor!