you're in luck. i've done hours of research as i recently bought a 1989 HBI rib. mine turns out to be a prototype put together by mercury/quicksilver with an HBI boat. they spent alot of time and effort installing an inboard jet system. i don't think anyone uses the innertube with the cover setup anymore.
i talked to the owner of HBI and he remembers my particular boat and had some suggestions for repairs of tubes.
he said to use a swimming pool liner repair kit as it is the same material. i found, however that with two larger punctures, i needed to form a glob all around and inside the puncture hole with a product called aqua seal(found at RIB dealership). then after it dries, put a patch over that. all the patches on mine seem to be holding and my son is bouncing on the tubes to test them for me
For my boat, HBI still has extra covers for the tubes wich they will sell for 1000 dollars each. i suggest testing the boat and tubes on the water for strength first before buying a new cover for a possibly worthless system. they do not make bladders anymore.
They said they would be happy to retube mine in hypalon for the "bargain" price of 5600 dollars! So basically you need to salvage those tubes.