How would someone begin the process of finding electronic manufacturers?
If I was going to custom design, i'd be going to maker meetups in your city, or applying to something like Hxlr8. There are also supplier/customer places that do matchmaking with additional services for a fee (HWTrek for example). I didn't use any.
Also, if you can find a Kickstarter of someone who did something at all related, ask who they used. Lots of creators are very happy to tell you!