If you referring to a 6.8 SPC...
Tim at Ko-Tonics has 20" fluted, long chamber, 11:1 chrome lined barrels for $265 and bolts for $60. You can use a standard AR15 bolt carrier available from many sources for $60-$90. (including Tim)
I am not aware of any other 20" barrel with the same features for anywhere close to that price.
Be advised that the 20" barrels from Tim will not be available once his current inventory is sold out.
He who snoozes ...loozes...!
As far as 10 round magazines..were all waiting for C Products to ship the 10 round mags with the new followers. The line forms at the rear...
HTH
Kerry