If you are looking to rebuild, you have to buy the whole thing. I have tried to rebuild one of the old Suzi vacuum operated petcocks before (the ones they made rebuild kits for)... that way lies madness. Check here for the how-to on the conversion to on/off:
http://suzukisavage.com/cgi-bin/YaBB.pl?board=tech;action=display;num=1113631600I wish I could get you another spring, but I just sold the old and busted petcock I had on here last week.