There is really only 2, Vista and Olin. Those are the owners of the 4 brands you are thinking of. They can control output how they want basically. The import primers seem to be vaporware.
The shop I usually buy reloading components from and usually has some of the most stuff in the area. Has hardly any primers other than 209s. They are selling them by the 100pk and limiting it to 3. Never saw it this bad.