I'll look at my princess auto regulator tonight to see what thread size the gauge needs to be and I'll pick one up for you at Princess Auto. I'll be at the meeting this weekend so I'll give it to you then. I should probably replace mine too so I can see an actual PSI. I've been getting accurate readings with my spunding valve gauge.
I think a decent gauge is about $9. they also have really nice liquid filled gauges for $15. they are extra big and you can buy them in 30, 60 and 90 PSI. I bought a 30psi max for my spunding valve...very accurate.
Let me know which one you want....I believe the cheap ones are 100psi gauges.