At the time of this post, not a single model railroad manufacturer makes a model of the AC44C6M, these engines are rebuilt Dash 9's with a GEVO cab and alternating current traction motors for those who don't know. I watched a video a few years ago that my buddy NSModeler24 made (yes, he's one of my friends from North Carolina), where he took a Scaletrains NS Dash 9, Replaced the cab with a Tier 4 GEVO cab (he kept the rest of the engine) and renumbered the engine.
I happen to have an Athearn Blue-box UP AC44 laying around that I haven't used, and I've started work to make this engine an NS AC44C6M. I already have a shell of a Tier 4 GEVO that I got off of Ebay for cheap. I'm planning on adding LED headlights, ditchlights, numberboards and walkway lights and a new ESU Loksound 5 decoder. I'm planning to number this engine based off of an AC44C6M I've seen, #4550.
Brand new by
David R. Collins, on Flickr
I will continue to post updates as this project comes along.