Fill Station in Tucson??

I have used Planet Scuba for a couple years until I got my compressor. They do 4500 psi but by the time you walk out it's more like 4200 due to cooling. $8 per fill. Tried to post a link but something went awry. Google will get you there.

The Dive Shop is another that may work. I have not used them but know others that have and recommend them. 

https://www.72aquatics.com/ is another, no experience with them but maybe worth a call.

http://www.disruptivepaintball.com/ is a paintball shop that does 4500 fills for $2 per 1K of fill pressure. Not sure of their filtering methods though.

Dive shops provide "breathable" air, nuff said!