A line of Tito Partisans would be great. I don't think the Handschar saw much action against any regular Russian troops much did they?
A few helmet head swaps and you could have yourself some Prinz Eugen SS troops as well. But then again, their "service record" is mainly against civilians, so they might not be the best subject for gaming. I doubt many of them experienced too many shots at them in anger...
I think other than those two, they were the only SS Gebirgs were they not?
A little trim to the feet and some head swaps again and you could use them for regular SS I suppose, or Gebirgs in the Heer smock would work too, mixed in with Brigades regular Gebirgs for a late war mix of uniforms. Lots of options here, not just Handschar!