Which one of these calibers would be the easiest to find and most economical to shoot?

Probably the .30-40 Krag. The .33 Winchester hasn't been loaded in 75 years--being discontinued in 1936 witrh a WHOLE SLEW of other Winchester calibers. Marlin manufactured its model 1894 CL some years back in .32-20, .25-20, and .218 Bee. All three of these rounds are still being loaded.