I bought one, a CH25, for about 1/4 of new. Particularly if you're going to be breathing on them anyway (internal and external mods) and plan to take it to bits, it makes starting with a Kohler at least as attractive as a new two cylinder Predator, which has poor parts and technical support (although Performance 670 has a nice selection of aftermarket stuff). Sources are E-Bay and the various Facebook forums, "Kohler Engine Owners Group" (covers the old, heavy, flathead K-series as well as the newer Command series), "GT Pulling Classifieds" (also has various Briggs on occasion), "Kohler Command V-Twin Parts", "Kohler Engines" and there are probably more. I just saw a RUNNING CH750 advertised for $500, a running CH730 with a bad crank seal (easy fix) for $250, A BUILT pulling engine, 43 hp on the dyno (unspecified RPM) for $2000. E-Bay prices tend to be higher than FB, but E-Bay sellers tend to expect to ship. Lots of new Kohler parts on E-bay.