Matthew Zenkar writes:

Is it common practice to have custom threading made for those cases
where standard threads do not meet the needs of a project?

Absolutely. Instrumentation is full of it. A common example is filter
threads on cameras.

You seem to have settled a lot of design questions prematurely, as if you
hadn't considered aspects like backlash and thread pitch inaccuracy.

Also, does anyone have any recommendations as to where I might get
this done (preferably by a professional shop)?

I design and built a lot of finely threaded parts for optical applications.

http://www.truetex.com/