Well, I've been on the hunt for these for a while now, and I finally aquired a few! Piggybacks that fit the UE Supershocks, made by Progressive Suspension.
I replaced the o-ring on the little metal plugs with a bigger o-ring for a better seal, as the old ones were letting oil past, and would have made for a messy setup. They're nice and sealed up now though.
The piggybacks were used, and had some nicks and scratches on them, so I stripped the anodizing off of 4 of them to use on this truck (I thought about polishing them, but just thinking about that made me tired, lol so they stayed dull...this is my basher truck though, so they don't need to be super shiny anyways. Maybe they'll get polished someday when I'm feeling more ambitious)
I'm still looking for a few more of these piggybacks, if anyone has some they're willing to part with :) I would really like to have some black ones that are in good shape, as I would not strip the anodizing from them if they were.
-Travis