I have a long cage Rival 1 mech with a clutch that i was going to put up for sale that would probably fit the bill. It has a small kind of weird issue with it though, it was an ebay purchase listed as 'new condition' however when it came to fitting I couldn't get it to consistently stay up on the largest cog on the cassette no matter what I tried. Took it to the LBS and all they could come up with is that one of the cages might be slightly out of line. I was out of the country so long I missed the ebay return date so now it's sitting in the parts bin.
Anyway long story short it would probably work well if your not going to try and use it with a really wide range cassette in the back (I was trying it with a 42) or you could try and repair it. Don't really know what to ask for it but happy to do it for cheapish if it'll work for you.
Theres a couple of pictures of it in this album: