You 'might' have a piece that came from the old Korean War-era 'Military Rest and Recreation' program, before it became 'Military Welfare and Recreation'.
You could check out various pistols, rifles and shotguns - as well as tents, fishing and boating equipment and the like - and I remember that all of those weapons were commercial and were marked with the organization's initials on their receivers.
Eventually, they were all sold via surplus channels.
In this instance - a Colt Letter is about the only way to prove that connection - though it's been my understanding that they were off-the-shelf local purchase items.