I don't own one, but I like to play emulated SNES games, so I went looking for one because I have to use my crappy keyboard. I managed to find two of them. One with all controllers, and one just the Multiport I think.
UPDATE: I have purchased the Gravis GrIP Multiport with 4 controllers for $20. Here's the link for the other one, it's $22, and you have to get the controllers seperate at $4-$6. http://www.oldsoftware.com/old_parts.html