I guess its hard to argue with success but I always understood the liquid in patch kits to be cold vulcanizing fluid and not rubber cement. The difference being that the vulcanizing fluid partially melts the rubber allowing the patch to meld with the tube as opposed to stick to the surface. A quick google search show a place in Rockaway NY called Patchboy that will sell you an 8 ounce can (with brush) for $9.19. If you keep the top tightly closed it would last quite a while so why bother with rubber cement which is primarily for paper?
Ridgewood, New Jersey USA