+1 Colt and Bravo Co. Mfg. barrels.
I have a Colt M16A2 barrel and planning on getting a Bravo barrel in 1Q of next year.
I also have a 16" LMT Defender 2000.
If you're just looking for now, also look at Sabre Defence from Talon Arms and CMMG also have them.
Also take a look at RRA, Stag Arms and Bushmaster.
I'm a former Washingtonian, maybe someday I'll go back there.
Good luck.