There's a huge scene here, but it's not very accessible from the internet. I'm sure you'll find it once you are here.
Also the Rocky Mountain Cycling club has rides all over the front range, there's usually 30-60 riders on weekends, with a broad range of participants from racers (probably no >3's) to brevet types to slower folks. There's some competition among the faster guys - but it's probably not a perfect fit for a racer. www.rmccrides.com you can do a few rides with them before officially joining.
We're a large, Denver-based team that rides and races regularly. Our cat 3 squad has about 20 guys right now. We generally roll out of either the Flagship REI store or the Starbuck's on Alameda and Downing just north of Wash Park. If you're interested, drop us a line on our team forum. My name's Jordan, and I'm the team director.