Have a state water heater model prv 40ndcto42dw, can't find a replacement for the gas valve. And the pilot won't stay lite.

Why do you think you need a gas valve? Have you tried to replace the thermocouple? If you are going to go through all these parts replacements, consider a new heater, otherwise you will still have an old tank and TPV

Agree ma. Start with the thermocouple and let us know if it works. If not, we will take the next step. Gas valves on water heaters are almost never the problem (does happen, but not often). If you replace the gas valve and it doesn't fix the problem, you have just wasted the money you could have used to hire a plumber to come in and fix the problem, and they probably will cost less than the new gas valve did.