Simple answer is anyone who makes suitable WW1/RCW Russians.
Copplestone does a dedicated pack but you are just as well using the Reds, shaving off the cap star and painting a red and white ribbon in its place. That's what I did. Only difference from any White/WW1 troops is no pogoni (shoulder boards). Buy suitable Reds and you obviate the need to file them off. Copplestone, Musketeer and Brigade all do suitable figures.