IMO "generic askaris" wouldn't work; there were many differences in uniform and webbing equipment. If one cannot accept paint conversions for, say, Late War German into Late War Austro-Hungarian, then why can one accept paint conversions for askari? Why not use WW2 Japanese for askari?

It's a wish list! Why restrict it any more than the topic title restricts it? So, I'm plumping for the German Askari already planned, and King's African Rifles to oppose them.