I think I'm going to draw up a business card that tells who I am, that I am a collector who can refurbish/fix old pinball machines, that also tells of how I'm interested in buying their pin, and find a place to stash it in the machine, either under the lockdown bar or crammed into the coin door somehow.
That way, the next time a see a great restore/fixer candidate, I can just drop a card in it and when they go to either remove a stuck ball or empty the cashbox, hopefully I'll get a call shortly after!