I want to build my own lights..

But I want drop-in parts, more of a plug-and-play style. Where can I get these?

fasttech.com, illumn.com, ledsupply.com, etc.

Well, where, for instance, would I get a completed unit of C8 pill with SST-20 emitter to go into a host?

Probably nowhere.

Older type-1 C8s used pills. Newer type-2 C8s have an integrated shelf.

Kaidomain has drop ins, but mostly for P60 stuff. You might find some old style C8 pills with emitters and drivers on Aliexpress. I see drop ins on there all the time. Also check the ones Lightbringer mentioned. Like he said though, the newer type C8 hosts don’t have pills.

I bought a bunch of Thorfire C8’s when they were selling them for $10 a piece a few years ago. If you can find any, they all had pills in them. I looked up complete pills and found a bunch on Ali but, they all had horrible emitter and driver choices. So I started just replacing the driver and emitters myself. Quite simple really. A few YouTube videos on it should get you up and running fairly fast.

Some of those are cheap. I bought one with a 7135 driver and xhp50.2 3v. I think the 50.2 was fake.

That’s more like “modding” than “building”.
Not that many lego-style flashlights since there are so many differences.