Finding a genuine Colt frame that's NOT assembled is going to be real tough.
In the rare occasion a Colt frame is found, it's immediately assembled into a working gun, so you don't see them very often.
If you want a shooter, Brownell's Gunsmith Supply sell a variety of "raw" frames. That is, new non-Colt frames used to build up guns.
These range from "drop in" ready to use frames to match grade frames that require a good gunsmith to fit them.
Many people use the "Essex" brand frame for non-match build ups.
You can get steel and stainless steel Commander frames from Essex or Caspian. New Essex frames are pretty good, but Caspian is still a step above. These are cast steel frames, but don't let that stop you. A well made casting is durable, if you don't think so, how many Browning High Powers do you see with broken frames? All Rugers use cast frames as well.