CC/Diemaco are great guns.
Some components can be sourced through civilian market and imported (primarily furniture).
At one point Knights was using CC barrels. The interesting thing about them, in at least the 15" or 16" barrel the British required, was that the mandrel used actually reduced the bore's diameter as it approached the muzzle, which increased accuracy/was required to meet the British SF's accuracy requirements. The longer barrel being the requirement to achieve desired velocity...
A few CC/D lowers have come onto the civilian market over the years, and at times Colt USA has used CC/D upper receivers in US-built guns.
Their monolithic uppers aren't available AFAIK.
US Marine Corp was working w/ CC to develop a new rifle, but I think that's been put on hold w/ some sort of weapon acquisition hiatus being put into place since the time of this article:
https://www.thefirearmblog.com/blog/2016/07/15/us-marine-corps-working-with-colt-canada/US MC partnering is a bit ironic due to the appeal to many of CC/D's ARs is that they rejected/never adopted most of the M16A2 upgrades that were primarily driven by US MC requirements, such as with elevation-adjustable A2 rear sight.