You've got a 30+ year old tractor that was Kubota's US entry into small tractors...with a non-US standard PTO. It wasn't known/popular at the time (I know, I had one). There wasn't much aftermarket stuff available then, and even less is still around. Kubota didn't even make much for it. Every once in a great while, a PTO reverser comes up for sale...and when it does, it's expensive...