CNG isn't really all that available anywhere AFAIK
. The problem is a chicken-and-the-egg situation...where companies don't want to install CNG sales terminals, since there is not much demand for it... and people don't buy CNG equipment, since the fuel is rather difficult to get.
As for gas stoves... CNG works a very diiferent pressure and volumes than do butane and propane, which will generally work with the same burner and hoses. CNG is not compatible with copper pipes IIRC, which are often used on boats with propane/butane setups.
CNG is not as good a fuel, since it is much lower in heat generated than propane or butane, but is a bit safer since Methane, the primary component of CNG, is lighter than air and will not tend to collect in the bilge or inside the boat to any major degree. Propane and butane both can collect in the boat's bilge and lead to a nasty explosion. I highly recommend any boat with a propane heating appliance, whether it is a stove or heater, have a propane fume detector, ignition safe bilge blower and a CO detector.
BTW, LPG, isn't always propane, but can often be a mix of propane and butane. Propane is a better fuel in the winter time or in colder conditions, since it remains gaseous down to about -40˚C, versus about 0˚C for propane. CNG is better in really cold weather, staying gaseous until about -150˚C.