Epoxy is a two-part resin and hardener system that comes in many flavors. Most boat builders stick with one of the major three: West System, System 3 or MAS. You can mail order them from the usual suspects, Jamestown Distributors, Hamilton Marine, etc (Google is your friend). Smiths CPES is an ultralow viscosity epoxy, Git-Rot is a one part wood hardener. All of them will work, you may find the standard epoxies more versatile in your shop.
Warming up the rib ends will help the epoxy penetrate.