I found one listed on Car-Part.com for $600+$100 core, but even then it'll need reprogrammed.
Personally, I'd grab a pick-up one with the same part number (they use several random part numbers on totally different applications) and let them flash it to your truck.
As far as the "purple plug" BS, 5.9 ECMS also have them, so the dealer rep you're talking to is FOS.
Mark.