Hyperkin just released the Specialist, a $30, 2-button controller that’s compatible with both TurboGrafx 16 and PC-Engine systems: http://bit.ly/pcespecialist
The Specialist is styled after the CoreGrafx controller and its simple layout consisting of: a d-pad, start and select buttons, II and I buttons and their corresponding (3-level) turbo toggles.
While I wouldn’t necessarily use the Specialist as my main PC-Engine controller, I’ll gladly add it to my testing bench.
I usually don’t speak highly of Hyperkin products in general, but throughout the years they did offer a select few decent controllers like the NES Cadet.
Hyperkin also released an interesting controller for the Atari 2600 called the “Ranger” that’s both a gamepad and paddle controller in one; A unique concept that 2600 fans might find is worth trying: http://bit.ly/2600ranger