I am seeking an original or replica. What do you recommend?

I think John Thomas makes some, but I'm not sure. If you can't find one, 607s also used the XM16E1 3-prong flash hider.

of course if you can get an original, that would be best...but can you get one?

just a quick google I came up with this one...Gen 1 - 3.5" (607)- Black (2nd from left is what you want)..you don't want those thick split washers though
https://retrorifles.com/moderator-flash-hiders-car-15-xm177e1-xm177e2-colt-commando-1963-1974/


ETA back when I was fooling around with AR's more, I had this made up for a 6.8spc barreled upper


was going to 607 it, but never got around to putting the stock on the lower