Hey, two stores in metro Denver:
1. Clear Creek Prospecting Supply, I-25 to 70th Ave, just west past. Broadway, S side of road. Been open a year or two. Host the local GPAA chapter and can sell you the membership pack. Run by a couple and another guy (who makes a lot of the sluices they sell. Real prospectors, Johnny used to run guided prospecting adventures too. Somewhat limited inventory but there for just one purpose - small scale mining.
2. Gold-N-Detectors, Washington St just north of Clear Creek in central Golden. Been there for many years. Have a wider range of products but quite a bit of focus on detecting too. Sells my favorite field pan, the Proline Professional. Owned by Louise but when Bill sold her the store, he never left! Every day he's on a stool in the back answering questions...but often tersely! Smart questions happily answered, newbies occasionally tolerated if they act humble ;-) They sell Angus Mackirk sluices which I like although not as much as I like Bazooka. Goldtraps!
Cabella's is also in town and they have a half aisle of prospecting gear but I prefer to support the local shops.
I recommend getting 20 and 50 mesh screens right away if you can afford to. Classifying makes finish panning soooo much easier. Also a good magnet to pull the iron sands out for separate prospecting.