Did you try pbresource.com? Call them up or shoot them an email. Even if they don't have the exact part, they might be able to suggest a substitute.
Also, keep your eye on ebay. For better or worse, somebody's probably parting out an old Bally and you might be able to find what you're looking for. If you see somebody selling new-old-stock Bally coils and other parts, you could message them and say "hey I'll give you $5 for some switches/brackets/whatever." Couldn't hurt, anyway.
What's the game you're working on?