Given the winter temps in Colorado, pretty much every gas station that I went into had Heet. I never saw it sold by the ounce anywhere, but given how little Heet costs, it's always possible to buy a bottle, keep 5 or 6 oz for your hike and then dump the rest (it just evaporates). If you did this 4 times during your hike, you'd probably end up wasting $5 or $6 on fuel that you dump.
That being said, I find that the western US is a bit dry (but possibly Colorado will not be dry this particular summer!). I have found that I prefer to use a cannister stove to reduce the likelihood that I'll inadvertently start a forest fire. As I recall, cannisters were available in Breck, Twin, Salida, Gunny, and Silverton.