Replying to I need same size balls different mass HEEELP!!!

I don't know if anyone can help out but here we go:

I need (for a trampoline math/physics applied project) balls (spheres) of the exact same size (ranging from 10cm diameter up to a metre) but with different masses: Ideally i'd need a set of balls of same radius with 1kg, 2kg, 3kg, 5....10kg. Although 5 different masses (but proportional, like 4, 6, 8, 10) would be fine, i need 4 different masses at least.

I've looked into medicinal sport balls, but can only find 2 different masses for same size...they evidently get bigger as they get heavier.

I also thought of filling a same size football with different materials, but that would get me 3 different weights max.
I need the minimum weight to be 500g or else it won't bounce on the tramp.

PLEASE PLEASE PLEASE help me out here, im going crazy...