One simple source for ether is John Deer Starter Fluid. This is ~80% ether. I like just mixing the JD with mineral oil in a small jar marked with the correct volume of each (25% oil). This fuel uses a bit more then kero based fuel (~ 15% more), but it is simple and always fresh. Some other Starter Fluids will work mixed this way also do some test mixes and try it out on a test bench to get the correct prop and compression settings.
Best, DennisT