Hmmm... I don't know about the availability of this one, but if Boggy Creek 2 and the Legend Continues was worthy of mst3k wouldn't the first one must be riffable too. I've got a long list but if it would be of interest I or someone else could take it on. I think it would be a great riff.
Did you know that "Boggy Creek 2: The Legend Continues" is actually Boggy Creek 3? True story.
Isnt that kind of like Highlander 3 pretending that Highlander 2 (they were from space?!?!?) did not happen?
Speaking of.......... HIGHLANDER
Yeah, first space, than the distant past, then forget it we don't know where they come from.
PS. I did riff Highlander II. Are you looking for a riff for the original? Man, you're going to make me do work aren't you. Okay, here' s my list as of now so it might be a while:
Batman
The Incredible Hulk (Edward Norton)
The Wizard
The Incredible Hulk: Prometheus
Sliders pilot episode
Hook (?)
Josh Kirby Time Warrior (chapters II-VI

)
Frankly, Highlander II hasn't sold so well so I don't know how the first one would do.