So, if I do plan on making my own, does anyone know where one can go to get some help? I already know that GamesX has a page that shows that the Twin Stick is a standard controller with the second stick rewired to the face buttons (B, Z, Y, X are direction and A and C are triggers).
And I have a couple of old PC flightsticks. In fact, if I get this one that they have at the Thrift Store, then I'll have to identical sticks. And then I can just hack them, rewire them, et al, and have two decent, though possibly ugly, twinsticks.
I found a site a while back on arcade joystick construction, it's got a crazy amount of information on the subject, some of which may be of some help to you. http://slagcoin.com/joystick.html
Specifically, the PCB and Wiring section has pinouts on Dreamcast, Xbox360, PS2 & Saturn joypad boards, and a list of suppliers for the joystick parts you'd need to build the rest of the stick.