I have a F1 silencer I made from a D cell maglite sized tube with internal threads on both ends. The threaded end has the baffles retained inside with a ring, so I have "thread adapter" end caps to attach it to different .30 caliber guns. I'm looking to replace the endcaps with some quick attach system. Is there a brand of endcaps that will fit D cell maglite internal threads and fit any of the more common quick attach muzzle brakes out there?

Should add: I need to support 1/2x28, 1/2x36, 5/8x24 threaded muzzles.

I've never built from a Maglite tube, but you need to be certain of the thread pitch. Is it an actual Maglite flashlight or one of the solvent trap sellers using Maglite sizing? Some are 20tpi and I think some are 24. Not sure if all the majors are the same, either.

Holding baffles in isn't an actual legal requirement, it's internet myth. Your end caps are silencer parts and not interchangeable. This is why you think long and hard about how you want to mount and adapt the device to your arsenal. There's a myriad of mounting options nowadays. Thread adapters

aren't silencer parts. This is why you choose the largest thread pitch, on a rear cap, and have multiple adapters. Or you can do QD mounts with a common type FH or MB.

Since it appears you've damaged your rear cap , you should send it off to an SOT to be replaced with a modular type piece that meets your needs.

I know it's not what you wanted to hear, but I'd rather see you play by their rules than get jammed-up.

Like a Griffin armament Taper mount? SD tactical, DM and I believe super precision concepts have a Taper mount adapter.
SD Taper mount adapter

Are you turning this into a "go be poor somewhere else" thread?

Or build a flash can that happens to use the same thread pattern.

DM, SDTA, and SPC all sell the end caps you're looking for.