I'm trying to find a place that either has the pots or will import them for a modest fee. I can't see spending an extreme amount for a try at making a controller.
My plans are to take the left side D pad and make that into a paddle controller with a switch where the N64's start button is. I was also thinking of making the yellow C buttons, at least the L, U, and R C button into the Start, Pause and Reset buttons. It's a bit of an ambitious project and I'm not much of a soldering person but I'm going to give it the old Try.
I've got a bunch of ideas, and we'll see how they pan out.