Flaming Gorge Resort Fly Shop, located on US Hwy 191 as you come in from Vernal or Manila, has the best selection and they are good about quickly restocking what they run out of.
Flaming Gorge Recreation Service Fly Shop located in Dutch John, has a great fly selection, and also has a good selection of tippet, floatent, ext.
Red Canyon Lodge has a nice little gift/fly shop with some unique fly patterns,and they offer friendly service and info about the area.
Green River fly fishing guides
Utah
Green River fly fishing guide
Utah