They're mostly used for targeting lakers or coho so you run them behind smaller dodgers, flashers, cowbells, etc... I personally haven't used them yet since we're rigged for either browns or kings.
Any of the trolling fly companies carry these - A-tom-mik, ITO, Big Weenie, Howie... With a single hook, I think it would just be considered steelhead trolling fly, not a peanut. Could be wrong, I've done more studying than fishing at this point but I'm working on that.