Ask around at local hobby shops. But here's a start (listed roughly in distance from Chandler):

http://www.azmodelaviators.com/

http://eastvalleyaviators.org/

http://slrcc.org/

http://www.sunvalleyfliers.com/

http://www.ampsrc.com/location/

http://www.arcs1.com/

There's a club at Scottsdale Community College as well.