Shimek's in Anchorage had 1 and only 1 of the proper 16-pin adapter left.
The kit came from Best Kits:
Part number BHA5600
I talked to the installer there and he recommended placing a unit between the speaker out and the factory amp that would allow me to adjust the output levels.
I am going to use the speaker out to the amp so I don't have to chop up and solder some RCA connectors, and also because the truck is loud and I can probably use the additional volume boost. He said that would work as well.
Now to break out the heatshrink and soldering iron...