I'm not 100% sure what engine this machine runs, i have a 3 cylinder kubota in my head but really not sure. I don't know of anyone over here that deals in second hand kubotas but i do know where to get good priced aftermarket parts. Depending on whats wrong with the engine you may be able to repair it or get the whole thing re-conditioned. 2-3 years back i got 2 V1702's re-conditioned. I got the machining for free, the parts cost $1000 plus the pump and injectors $400.
If the head is cracked there are people that repair them as well.Or you can get a new one, but expensive.
Any ideas whats wrong with the engine? any reason that you can't repair it? unless it threw a rod.