You don't necessarily need to use a Kohler engine on it. They had Briggs, and Tecumseh engines that ran fine for many years, with usual care.
Just remember to use an engine that has all of the drilled and tapped holes in the crank-case, where things must be bolted onto a replacement engine. The engine mounting bolt holes should be the same. RJ

Thanks Rusty, I guess my note is confusing. I don't need a replacement motor, only a carburetor for my Kohler engine. The engine was running well before I knocked off the carb. SS

Check your small engine repair shops.
Maybe they have one cannibalized from a blown engine??

Go to smallenginewharehouse.com I believe that is there web site or look up small engine wharehouse and they have engines for Troy Built Tillers.