I know that Bushmaster sells them:

http://www.bushmaster.com/shopping/barrel-assemblies/abbl-20a2.asp

What are my other choices?

Not trying to be an ass, but you really don't need any other choices.  Bushmaster offers both post-ban and pre-ban 20" gov. barrels with chrome, 5.56 chamber, 4150 steel etc. If you are looking for something special, have Kurts Kustom Firearms set you up.

CMMG, Inc.   [url]CMMG.com[/url]

There's some 20" chromelined 1/7 FN barrels on ebay right now.(yes, real ones [rolleyes])

Thanks for the replies,

I went to the CMMG website and saw the:

"Unused Chrome Lined USGI 20" 1/12 pencil barrels"

http://www.cmmginc.com/cmmg_images/tbl_images/Barrels/20_Lightweight_Barrel.jpg

for $185.95.  These look interesting, but it says "1/12" rather than "1/7."  Also, they do not appear to have the same profile as the illustrations of 20" barrels I see in the TM9-1005-319-23.pdf M16A2 Technical Manual I downloaded from this website (e.g. pg. 60).  Are the CMMG barrels of M16A1 type?

The barrels in the manual appear to be narrower under the handguards than between the muzzle and the front sight.

Bushmaster's description of the post-ban version of their "20in Government Profile" barrel has more detail about their dimensions (they are narrower under the handguards):

http://www.bushmaster.com/shopping/barrel-assemblies/pbbl20a2a.asp

Bushmaster's catalog (pg. 36) calls their pre-bans "M16A2 Gov't Type."  Does CMMG offer an M16A2 type 20" in 1/7? For $199.95?

not everythign is on their website. drop them an email and they'll hook you up. CMMG is a pro outfit and they will take care of you.