If you are looking for US parts for 922 compliance there is little available.
FWIW Sign up for CNC warrior's out of stock notification. Last year I received an email for restocked part there - I could not even recall making the request LOL - it had been a long time. They seem to be a peculiar operation - strange production schedule.
On the East German NK hider JMAC used to offer a two port and a mult-iport variant. When they stopped I inquired about them - was basically told no and don't ask again.
There are Russian made RPK long flash hiders and RPK74 hiders available on gunbroker - I just checked - still there.
There's a guy by the handle "brick" that used to offer a US replica of the long RPK hider. I obtained one on the secondary market - well made.