There is a pressure release valve down below on my gas water heater where can I get a new one

Its on the bottom side of the tank it is leaking

That's the drain, for flushing sediment if its on the bottom... the pressure release valve is high on the side. But its called a safety valve meant to prevent excessive pressure.

If it is in deed the drain valve that is leaking, you can purchase a hose cap that will screw on to the valve (just like a hose) to stop the leak. Only a couple of dollars.

Harold and I seem to know the old $1 trick, just cap it with a garden hose cap.

Hi casimria and welcome to The Plumbing Page at AskMeHelpDesk.com
Where's the leak? From the spout? From around the stem? Let me know, Tom