I've never found it here, so I would be interested too. I've always had to get it at Fairway on LI when I visit family.
Verjus is invaluable when making sauces for those who cannot have alcohol - when cooked, it offers a reasonable approximation of white wine, but without the alcohol.
They have it, also a interesting choice of vinegars and molecular cooking ingredients. You won't get it by the weekend.
I would give Fromaggio a call and then maybe Butcher Shop in South End as a wild guess. I never saw it at Wholefoods ....