The 14 HP air cooled Kawi used on the GT242 looks to be out of production and sold out at most places. I would call either one of the above suppliers to find a suitable Kawi engine to retrofit, and take advantage of probably being able to upgrade to a 17 HP engine in there. That is one good thing with vertical shaft engines, finding retrofits is much easier than with a horizontal mounting. With vertical shaft it's mainly just finding similar outside dimensions and the right length and width of the crankshaft end. Then it might only involve drilling some new holes in the mounting plate, hooking up control cables and wiring and away you go.
-Fordlords-