Think it was Red Barn Armory at least but can’t seem to find their site anymore.
Anyway you could pick and choose nearly every part you wanted in the LPK so you did not end up with extra cheapo safety selectors, bolt releases, etc. since you were just going to replace them anyway?

Most of the LGS around here sell AR small parts. I just go in and snag all the springs that go sproing, detents, etc. and stock my parts drawer that way. Saves on absurd small parts shipping fees, but the parts are a bit more expensive, so net savings is nil, but at least I don't have to wait.

I'm sure some of the Cincy/NKY shops do the same.

I just buy Wilson Combat's small parts kit. Everything there works for me.