You should try Meetup.com, there are quite a few mommies groups in your area, I live in the Broomfield area. I would sign up for a lot of the groups and then try going to each of them a couple of times. After trying 4 different ones I was able to find a great group that really fit me and my childs personality.
Other fun things in your area to do on your own are, Kangaroo Kingdom in Lafayette they have open playtime available, The Curious Cup Coffee House also in Lafayette has a small play area and soft sofas for moms, the Broomfield rec center has a free indoor play area. The WOW Childrens Museum is in Lafayette and has fun things to explore as well as a story time. The Erie Community Center has a nice pool with slides and a play area in the water. You could also try the local library for story time, I think that Lafayette's is on Monday mornings, but that might have changed. It has been a while since I went to that one. St. Vrain Memorial building in Longmont also hosts something called Itty Bitty City. It is an open gym playtime with push cars, balls, kiddy skates, things to climb on etc...
Hope this helps, I know how hard it is to move to a new area and not know anyone.
Good luck,
S.