I used to live in Boulder and bought my first game (Joust) from Jeff at Tattoine Electronics in Cheyenne, WY. He had a lot of games then and had been in the business a long time, but that was about 8 years ago. He is a good guy, tell him I sent you and I am nearly certain he will remember me- if he hesitates tell him "Zach the dude you sent the 720 to Michigan for" (that was my third game). He is a good guy and will probably think you are nuts if you are overly excited about arcade games, which I always found funny.
There was also a place in Golden that sold games. I think it was called "something" Trading Post.