The last time for me, I got my 2003 Tonto National Forest (TNF) parking sticker at the TNF office at 2324 E. McDowell Road, Phoenix. Tel: 602-225-5200. I headed west on I-10, north on N. 24th street, west on E. McDowell a short way. It's on the right (north) side of E. McDowell.
I called the TNF office in Phoenix and they said they had the 2004 parking stickers in stock. As someone already posted, the sticker runs 12 months. They're good for 12 months after you bought the last one. They're not only Jan-Dec stickers. 8)