Getting kind of late for potatoes, but I've found them at all the area Agways and Global Ags (tho' some stores have a more extensive selection than others, and I've found that Yukon Gold's sell out quite fast).

I happened to be wandering around a WalMart a week or so ago (not a normal place for me but I was looking for emergency auto repair parts and the local store was out of stock) and was surprised to see they sold seed potatoes, bagged and packaged like flower bulbs (5 lbs. I think). Don't recall the price but seem to remember it wasn't a particularly good deal. They also sold asparagus crowns in small quantities (10 per bag, I think).

If you're still looking for seed potatoes, Parker Gardens has them. They are on Terrill Road, Scotch Plains.

Here is a link that might be useful: ParkerGardens web site