Henry, Kohler and Kawasaki do make, sell and market currently available water /liquid cooled V-Twin engines in the power range you want.
You can search these up on Internet offered small engines for sale sites.
For a time APL/GEK did use this engine.
Another dandy is the small 3 cylinder inline Kubota water cooled natural gas engines.
Quite a bit more money but with Kubota world-wide service and parts.
Both of these engines choices are coming available now in well used yard/garden/light industrial equipment systems now.
Ha! Ha! Search up water cooled riding lawn mowers.
S.U.