Jacks Ball, but not quite.

We are looking for a supply of a 0.680" diameter foam ball. Like the little red rubber ball that came with a Jacks set but not as dense, and my kitchen sponge is not dense enough. UV, bounce, temperature, and chemical resistance are not issues, resistance to air flow is. Maximum quantity would be 5000 pcs, and the project is cost critical so we prefer to find something already in production. Any advice anyone would care to share about where we might look for something like this will be greatly appreciated. Thanks, K.