I doubt you'll find many flip-flop wheels that are 135.
HOWEVER, a good (and super-cheap) way to do it is with a bolt-on cog on a disc rear hub. With a cassette cog and spacers, you have freewheel on one side, and the bolt-on is fixed on the other. No respacing, redishing, or any of that. However, you may have trouble finding a disc rear wheel that is compatible with rim brakes.