You might be able to build a miniature gas powered generator. There's no production unit that small, but I think one could be built from a glow engine and a rare-earth brushless AC motor that would deliver the power levels required. Of course, this begs the question of whether it would be smarter to try and run the props directly off the engine and save the conversion losses and associated weight of the regulator electronics.
If there was an available miniature fuel cell this might work, but I don't know of any on the market, and the power levels from the lab devices have not been impressive.
Solar probably isn't going to do it, the surface area you would need would be an impediment to vertical flight.
Compressed air could work for short flights - the power level is high, but the energy storage is low.