Best thing that you can do for your gadgeteer is kill crock, cuz I never had him sell his gadgie items, but they're on him when you kill him. If you're patient, Anna will have the electrodes and duct tape. For the Porta-Potty, both items are hidden, so make sure you are searching or that you have a ranger...
Here's the address to Jandrall's site, with spoiler info on gadgets. There are some things, though, on the site that never made it into the game, like the shadow hound gadget and its parts. Cheerio!
http://www.geocities.com/jandrall/