Don't know if this will help, but I ran across this when I was considering buying an old bike to fix up. The forks were damaged, so I was trying to see what my options were for fork swaps. In a nutshell, the guy uses a site that matches sizes of steering head bearings, another site that lists stem sizes, then compares to the original site to find every other bike with the same measurements. Basically, you can find every possible front end swap for your bike.
I can't endorse whether his system works or not, but it looks good in theory to me. I ended up not buying the wrecked bike, so I never got to test it out myself. Maybe some of the guys with more technical knowledge than me can verify whether this will actually work or not.
"Great info source for matching steering stems, fork swaps." - Tech talk - General bike talk - Vintage Street Fighters/Customs/Specials - Message Board Yuku