Damian Yerrick has made demos for the standard controller through Four Score, the Zapper, the Super NES Mouse, the Arkanoid controller, and the Power Pad. He's interested in making demos using the following controllers but lacks necessary hardware to test them. Owning this hardware would allow documenting additional details of their operation here on the wiki, such as the ~8 ms ADC delay of an Arkanoid controller.
These controllers have been acquired but not yet implemented
He'd need one of these plus documentation (from here, Martin "nocash" Korth's Everynes, or emulator source) to get started.
All these appear to be documented to some extent in Everynes. But he'd need one of these plus a Famicom and either an EverDrive N8 or a "TNIOJ" adapter to use a 72-pin PowerPak.