Found a valve on Amazon
pressure releif valve amazon.JPG
I ordered one. If anyone adds a relief valve, be sure to also install the Safety Valve that is included.
https://www.amazon.com/Pressure-Cook.../dp/B00BM2CC2Y
The titanium lid is not easy to drill through to make the holes needed. I have punches to make the holes required. Just wanted you to be aware of this.