I'll vouch for The Custom Foot. They were honest with helping me out on a foot/boot issue and I ended up buying their insoles. They do carry Lowa and some others and will also measure your feet for a proper fit. I do believe they charge for it if you don't buy their boots but IMHO it was money well spent. Just an FYI, it's still ski season and they are probably still slammed right now if you go in on a Saturday.
Other CO stores,
Bentgate Mountaineering in Golden. They have a website as well and run some pretty sweet sales. If you have big feet, like size 13, the selection is limited in the stores.
Neptune Mountaineering in Boulder. Good folks, knowledgeable, not sure if they carry Lowa but they have Scarpa, La Sportiva and Hanwag.
Sierra Trading Post has a store in the Littleton area. Not sure what they'll have in stock though.
REI's become a joke.