Hi mate, I had the same problem. Ordered a 2 bolt brake booster from Tarty thinking it would definetly fit and it turned out my spacing was around 90mm! So, when I returned it to them I asked if there were any alternatives and they said there weren't..
Making/getting someone who has the tools to make a booster for you seems the best option. I do have some tools to make stuff, so if all else fails drop me a pm and some plans!
Cheers, Tom