Scientific American had an article on how to build your own CO2 laser from a neon sign power supply, using a refrigerator compressor as a vacuum pump, etc. many, many years ago. Like so many I hesitate to name the decade it was in. I definitely had the article in my possession some time before about 1995, but I don't remember how much older it is than that. (definitely about...see how clear my memory is) It seems to me that I may been keeping that old copy around for a few years (or somewhat more) before then.
Or you could just enter laser kits (or CO2 laser kits) in a search engine like Google, and find sites like http://www.repairfaq.org/sam/lasercc2.htm#cc2hbl