yes any audio store should have it. they come precut and wired. just be sure to pay attention to colors i know some change from what head unit you will be using.
Actually for the Rockford system it uses RCA jacks that come out of the harness. The actual wires you use are constant power (yellow), the one that turns the unit on(Red I think), Remote (blue) and you have to make a new ground (It doesn't run thought the harness) I don't think I'm missing any there. All audio goes though RCA cables (4 channels - 2 front 2 rear). I ordered my headunit from cruchfield so it came with all of the wiring.
I went the crutchfield rout also, easy peasy, you will have to splice a harness together, but it is an easy job. It is so the harness of the radio pluge into the factory harness of the truck.