They are pretty readily available, but there are two kinds.
One is just the choke heater, but the other comes with a thermal switch and costs more.
If you don't have a "power only when running" place to go to, get the switch kind. If you have an oil pressure switch for the fuel pump, that is good.
If you just tie the non-switch type to the ignition and you have a hard start, the hard start gets worse fast.