I work in Boulder, so I have been buying my fuel from Bartkus Oil on old Pearl Street. There are a whole bunch of new distributors that might be more convenient for you, depending on where you travel. From the Blue Sun site (www.gobluesun.com):

Poudre Valley Co-op
225 NW Frontage Road
Fort Collins, CO
(by the auction place, NW of the Hwy 14 interchange)

La Salle Oil
320 N 1st Sreet
La Salle, CO
7:00-4:30 M-F, 8:00-12:00 Sat

*** Oil Company
555 East 8th Street
Greeley, CO
7:30-5:00 M-F, 8:00-12:00 Sat

And there's several retailers in Boulder and Denver, if you travel that way.

Try a tank full, you'll agree with my experience. Good Stuff.