This is another style, on a Montreal headlight cover servo. Not sure which would be applicable to your brake booster, though. Have you tried those restoration decals from CarClassic or those you occasionally see on eBay? Someone in here must have an original early Bonaldi brake servo ...
I didn't see these labels on my 69 GTV (but that doesn't mean they weren't there when it left the factory). But I've never seen any photos yet showing these labels. Also, you might want to post this question in the Spider or GTV forums (I never saw this post before today) and I'm guessing that many guys probably haven't subscribed to this forum. That said, I wonder who else may still have these on their boosters?
There is a guy on ebay that goes by jmduncan01 that I have bought many decals from. I can tell you the quality is top notch! He doesn't seem to have anything for sale at the moment, but if you contact him I'm sure he will get back to you. I needed an ANSA decal for my muffler and he made me a few after sending him the image. The decals are even guaranteed for life! If they go bad for any reason he will send a replacement.