Comp cams has the ends, 5/16" and 3/8" cups and balls. They also sell 10" lengths of .080 and .120 tubing.
All told though, by the time you by the cups at $50.oo a set, the balls at $40.oo a set and the 10" x .080 × 16 tubing at $130.oo a set you most likely would be better off time and money wise just ordering a set.
Now I do think it's a good idea to have a set of cups and keep so.e in the trailer for race weekend. Never know when you may need to make a repair, cut down a old long one, etc.