Seriously, though, probably the only muzzle device that is safe, legal, and fit-for-purpose is a thread protector.
Nordic Marksman has the OEM part on their website, but they're not showing any in stock. <https://www.nordicmarksman.com/Glock-Barrel-Thread-Protector-9mm-M135x1-LH.html>
Elwood Epps has an AAC in stock. <https://ellwoodepps.com/advanced-armament-corp-thread-protector-m13-5-x-1-lh.html>
You'll also want to get some o-rings (that'll fit the groove in the barrel); they'll serve to keep the thread protector secure, and where you want it.