To assemble, you need a punch set that includes some small punches, some tape, a needle nose plier, small hammer, long handle screwdriver (flat or philips, depending on the kit), a large plastic ziplock bag (to catch flying springs), a protected surface to work on, and a few wood blocks to elevate the receiver when punching pins. To properly install the stock, you should have a stock wrench to tighten the castle nut. I have that tool if anyone needs to borrow it. To torque it properly, an AR lower vice block should be used along with a table vise. Again, I have those. You can come over and use those. It'll take 10mins to install that.
Source: Amazon.com
Source: CheaperThanDirt.Com
Yes, receivers are a serial number item. it will need to go through a FFL if purchased from a retailer or shipped into AZ. If you purchase from a local private party, then no paperwork is required. I always suggest a bill of sale, though.
AZ has many AR manufacturers. You can check most small gun shops. Check "Phx.Backpage.com" or any firearm forum under the Buy/Sell pages. I also look to Gunbroker.Com and see if there are any local dealers.
Here's a guy in Prescott that's selling on Gunbroker. I could contact him for a local purchase. His contact info is on the auction posting.
http://www.gunbroker.com/Auction/ViewItem.aspx?Item=245898172
As for ammo, J&G has surplus. For better ammo, look to this special at Cabelas. They have the
American Eagle Black Box for $5.49. Good ammo. Go to their web site, get the
$20 off code, then order online to save some money. Have it shipped to their store for pick-up, then they won't charge you shipping.