Hi Roger, search eBay and Craigslist Denver daily. I found a great deal on a dredge this winter from a party in Colorado (and the guy threw in a bunch of extras!).
As we get closer to spring, I'll bet more start popping up. Not sure if you're looking for a highbanker or floater.... but I assume floater since you mentioned air.
Here's a pretty new looking Keene highbanker on eBay for example, but it's already got a lot of interest (reasonable shipping):
Keene on eBaySaw this on Craigslist Denver, but again... probably not what you're looking for (good price though if it runs):
Backpack Dredge on Craigslist DenverI'd keep checking eBay and Craigslist at the very least.
Good luck, and let us know what you find! It took me a couple months but I eventually found and bought what I wanted for a great price.