Since you're in Maricopa county, you can take it doen to Sherrif Joe. They have a lady (I think her name isJane) that handles all of the form 1/4 signoffs. I don't have the number handy, but if you call their main number and ask for the NFA section, they can transfer you. It's a bit of a pain to do because you have to fill out an MCSO questionaire that is pretty similar to the form 1/4 that you are doing. The MCSO form also needs to be notarized. I usually take mine across the street to Wells Fargo bank. MCSO will also fingerprint you, but it will run you $8 per card IIRC, and you need to turn in an extra one to MCSO for their local background check. When you call, talk to the fingerprinting section as well, they have odd hours for public fingerprinting. Once everything is said and done though, they take about a week or so and then give you a call to come down and pick it up.
-John