You might be able to find something thru this Seagull site. It’s something like this site, lots of good information and helpful people.
http://www.saving-old-seagulls.co.uk/
If you want to try repairing your petcock, here’s how I did mine.
Since the original leather-like sealing material was cracked, brittle, and leaking all over the place, I made a new brass plunger and fitted a couple O rings to it. Then it got soldered to the original knob and it doesn’t leak a drop now! 😀
