Reddit mentions of RetroArcade.us Arcade Game Controller USB Interface PCB Kit for PC (MAME) / PS3 to Mame

11 of these 24mm buttons (You can get any color, the buttons just need to be 24mm)

One 30mm button

PS3+PC PCB (You can pick a different PCB, but this is one of the cheapest. I use this one for my personal build)

Finally, you'll need a case.
This website by far has the best custom cases you can buy. They're upwards of $70, but look great. This is what mine looks like. Just make sure that if you order from here, you get the hitbox button layout top.

Your other options for a case are to buy a different custom one online, or to make your own. I did the latter first. As long as you have the tools, it's really cheap and can be a fun process. This is the video I followed for doing this.

http://www.ultracabs.co.uk/arcade-usb-interface-71-p.asp

A couple of people sell these - and they work pretty well.

Or you can just buy an ipac - much more flexible, more inputs, and much higher cost.

http://www.jammaboards.com/store/pc-mame-ps3-to-arcade-controller-usb-interface-pcb-kit-pc2jamma-usb.html

http://www.amazon.com/Arcade-Game-Controller-Interface-MAME/dp/B00F1YQ3DI/ref=sr_1_5?s=toys-and-games&ie=UTF8&qid=1413999897&sr=1-5

I just bought the joysticks/buttons off amazon. Wired them up to this board here: http://www.amazon.com/gp/product/B00F1YQ3DI/ref=oh_aui_detailpage_o04_s00?ie=UTF8&psc=1