I believe most NG gens can also run LP with a conversion kit (different jets). Might be worth keeping one of those kits around in case the NG goes away.
I have a 800w gen with a Subaru motor in it. It is NOT quiet!
These guys sell conversion kits,
Generator Conversion Kits to Propane and Natural Gas.
If you convert a gasoline gen to a NG one it will produce less wattage though. Not sure about LP to NG though.