Yonks is pretty classless. We use in as in 'for yonks', or sometimes 'for yonks and yonks'. 'I've been doing that for yonks.' 'I've been waiting for yonks.'

I don't think of it as being regionalised, but then I'm only in one region! (about halfway up the lefthand side). And I've no idea where it came from, but I've certainly been using the word for yonks.