http://www.nubytech.com/wp-content/uploads/2015/02/streetfighter-controller.jpg
This thing? It is not the same d-pad. Overall its a Good D-pad, very similar in style and design but if you have the two side by side, you notice the differences.
Most if what you find here are work logs and still photos, producing half-way decent videos is a bit more challenging.
That said, find anything thats similar, study and take notes. You notice alot of controllers are build on the same basic designs.
You have controllers without any encoders like old Atari 2600 joysticks, Sega Master system pads and the Neo Geo AES/ CD controllers.
And then you have Controllers with an Encoder, and that is pretty much everything else. You got simple encoders like the NES has which is just a parallel to Serial Shift register to straight up USB devices.
All the pads worth wild to hack are what we call common ground, meaning they share all the same ground/return voltage lines.
Good place to start reading is Slagcoin.com, it holds alot of basics to pad hacking, and you can work your way from there.
95% of everything is basic electrical, and you only have to get into circuit design for a few odd-ball/ troublesome boards.
Examples would be such as Trigger inversions, having to add diodes to signal lines, ect.