FWIW: I have purchased large quantities of paint from Mark at RAPCO in the past (personal use and group purchases). In each case, he discounted my per gallon cost quite a bit when the order got large... Also, as mentioned earlier, the truck rates were much lower for my entire purchase on a per gallon basis than the Hazmat charges from UPS would have been. Mark will also add spray cans to your order and shrink wrap them onto the pallets with the cases of gallons.
I'm sure that AJP will as well...
I've also talked to Randolph Products, but they couldn't get the colors/quantities that I needed the last time I did a group purchase.
Good luck with it.