Cant help you for contacts but suggest that if you look at manufactures of self righting frames, they are similar in having to cope with very high stress loads.
The other place you could try is Ribtec. I belive the Camel Boats, which I belive were built by Ribtec, had frames capable of carrying kayaks. Try them, they may be able to tell you who made theirs, or even supply them
Just a thought though, dont forget to take in acount the height/weight/g force calculations as 500lbs, X feet in the air, together with the way RIBS get used could put high loads on deck mounts, structurs etc.