Where do you all buy parts?

Hi all, I'm new to this community and this is me attempting to participate.

I've been repairing and building bikes for a good long while now. Mostly I bought parts off of Amazon or my local bike stores but I've run into a bit of an issue finding a bullhorn bar-end brake-lever/shifter combo for a 1x8 road bike. I can't find anything being made currently anywhere. I'm even starting to consider contacting some local machinists I know.

I guess this is the danger of endlessly customizing bikes to the point where you want to do stuff no one else has any interest in doing.

So let me know where you guys get parts and what your favorite procurement methods are for rare stuff.