We managed to pull together over 40 balls, so I guess we can reveal the location that we found that a ton of balls (it required a bit of travel and multiple stores) But we found the store chain
Five Below to carry the 7" POOF Foam Basketballs, the price? Under 5 Dollars,
Five Below Stores however are only located in 47 locations in Pennsylvania, New Jersey, Delaware, Maryland, and Virgina. So use their
Store Locator to find the one closest to you. (We raided 3 in South East PA) And all of them had better deals than any internet site I've seen. The best part? No shipping wait time or fee.
Good Luck