How many Ad agencies?

Good morning ad folks,

I'm hoping you can all help me with what I thought was an easy question....

How many agencies are currently operating in Colorado?

I was doing a speaking engagement at one of the colleges' marketing student groups and I got the question and didn't have an answer. So far I have contacted the Secretary of State's office who told me they cannot segment their business list by NAICS - which amazes me since we all have to list it to register. As well as, the Colorado Department of Revenue - where we all also register - with no response coming from them yet.

Any ideas on where to track down the info?
Ross