BB Bastards, when I can find the weights (0.25 & 0.28).
Airsoft Central EPS, again, when I can find the weights (0.25 & 0.28).
Otherwise, I'll hit an oversea store for the weights - usually golden ball and madbull.
TBH, if I could, I'd purchase a bulk quantity - between 50K-100K - just so I don't have to worry about supply. The problem is the supply ain't really there.