Tumbling Dice have an extensive WW1 range, no pics online really and the site is a little sparse on details but the old catalogue is
here. I have some of the Russians in greatcoats with fur hats and they're fairly nice.
I'm a bit of a newb at BoB but with the various types of headwear in the range I imagine you can fudge it for many forces, if you're not too bothered about complete accuracy.