Organizations:

Vegan Outreach (home of Why Vegan?)
Compassion over Killing
Animal Defense League of Arizona
Citizens for a No-Kill Tucson

Online Stores:
Vegan Essentials
The Vegetarian Site (lots of good information as well as products)
No Sweat Apparel
Alternative Outfitters
Downbound
Couch Guitar Straps
Zappos (has a large selection of non-leather shoes)

Other Resources:
Tucson Vegans Yahoo Group (free Yahoo Groups membership required)
Tucson Vegetarian Meetup Group
Tucson Raw Food Meetup Group
Post-Punk Kitchen - great vegan recipes