I've been looking for the same things for years myself. Check out Hinomoto - Compacts - Parts they have some head and engine gaskets. Also Southern Global has main & rod bearings. As far as a complete kit, I have yet to find it. I have not called to ask if they can get more than they have on their websites .
Mitsubishi MTE2000D, Dig It 258 Mini Ex, Deere Z930A ZTR
I know it can be hard to find parts for some of the Hinomoto, Allis Chalmers and Duetz Allis models. I'd give We are a Mitsubishi Satoh compac a call and see if he can get the U.S. unavailable parts from Japan