I was able to repair a Sevylor 2 person on a recent trip using a PVC patch kit I put together for my clear drybags.
I used a tube of PVC adhesive purchased at ACE hardware (product is called INFLATABLE REPAIR KIT in camping section) and some sheet PVC material intended to be used as glazing material (also purchased at ACE) My repairs was smaller, a couple of seam blowouts due to over pressure, but the patch and adhesive proved compatable. The sheet vinyl came in a 24" wide roll or a 36" wide roll, cut to order by the foot.
For a larger repair I would try HH-66 vinyl cement. Might be able to get it at Down River Equiptment near Denver, or use the link below (link also has clear window vinyl)
You might also check out the 'heat sealable taffeta' at Seattle Fabrics. This material can be heat fused with a household iron, might make a good iron on path for the outer cover.
Ripstop, Oxford, PackCloth, Cordura and other nylon and polyester fabrics!
I don't have any personal experiance with the HH-66 or the heat seal fabrics, just giving you the benifit of some of my internet research...found out about these in an article on making your own float bags.