Trzmielo and I were for +10 years persuading Ceasar Miniatures to produce such sets and they repeatedly decline due to I suspect political correctness and national embarassement factor. I doubt if they ever produce even Chinese communists, not saying about militia or warlords.
These are great ideas and could easily be a whole range. It would be nice to see Japanese in cold weather gear as well. Would open up a whole wealth of historical scenarios - Japanese v Nationalists, Japanese v Communists, Japanese v Russians, Nationalist v Communists, warlords fighting alongside or against the political factions. Good chance to have pre-war and early war rubbish armour on the table.