Hey Amigo, I'm from Buffalo and I married a Mexican. We had a pinata at our wedding in Mexico and I would say that most of the Buffalo Mexican stores don't really have a good assortment of what your looking for. Some good things yes, but not really pinata candy.
Try this. It has a good selection of the things I had in my pinata and I have eat most of it. Some candies i would add to this, Kranky K, Mazapan, BuBu LuBu, Obleas and of course Glorias.(the mexicocity restaurant in hamburg also has some of these)
I would recommend adding some off brand American candy to the mix because some of it is quite different and you want your guests to be happy.
Also, I'm going to Mexico next week returning for the 4th, if your occasion is after that, I would be happy to bring you a pinata mix bag.
(Swinkles are real good, but for the love of god don't put the slasaghetti sauce on it)