Hi Paul,
Good question. I know finding quality contractors can be a challenge.
How did you find the 5 contractors you already tried? How did you approach them? Did you issue them the plans with a spec? If so, that might have been a bit daunting to them. Not all GC's are capable of working through such a spec and plans as such. A GC that is a builder is going to be more comfortable with it.
Did you get them to the property before delivering plans? That works to your advantage, it gets them invested with time in the project and plants the seed of possibility in their mind. Discuss what you need done first before handing over the plans and spec.
As anything else, getting a referral for someone usually works best. Also driving around and finding other similar projects in scope can help you locate a GC to use. You might find one at your REIA meeting. While I prefer craigslist over the phone book, in this case the phone book may work better for you. Look for the larger ads. Ask your architect who he has worked with in the past.