You'll find very few gassrs for .60 and smaller airplanes. The problem is weight mainly. The RCS-17 that was mentioned is one option as are alot of the 20-26cc gassers out there. They will be heavier than a typical glow engine though especially once you factor in the ignition box, battery, and so on. For some planes that is not a problem and a few actually need the added nose-weight. Many will suffer from the extra pork though. Saito makes a 1.25 4-stroke gasser but I've only seen one in action. Looks like a nice engine but pricey.

I really like gas but for .40-.60 planes, glow is probably a better option. Electric is also something to consider if you hate the mess. You might also try a different engine. For instance, the OS 4-strokes seem to be much cleaner than the Saitos and some others.