They're available for around $90 per year at the Tonto National Forest offices. They used to be good from Jan. 1 thru Dec. 31 but I hear they're good now for a full year from the day you purchase it. I could be wrong on the last part. The Mesa branch has moved to the Higley & McKellips area.
Here's their website. Try giving them a call. http://www.fs.fed.us/r3/tonto/indexy.html