For the NKP, you have a very wide choice of everything but F units, since the NKP never had any. The most common models painted for the NKP are GP-7's GP-9's, SD-9's, SW 800's and SW 9's's. These are all made by Atlas. PA-1's are available for passenger service and you can still find some Athearn units in the Bluebird scheme. In the more exotic realms, there are Alco S-2 and S-4 switchers. Alco also made DL-701, RS-3's, and C-420 roadswitchers for the NKP. Just after 1960, the NKP also bought GP-30's and GP-35's until the merger with the N&W in 1965. The GP-30 by Bachmann can generally be found on e-bay at a reasonable price. There were also a few odd Baldwins that I think were only made in brass. So, you can usually find the GP-7, GP-9, GP-30, SW-8, SW-900, and PA-1 pre-painted in the NKP scheme. All the others you'd have to do yourself. Getting a black undecorated unit makes things pretty easy since all you have to do is add the road names and the stripes. Thae later simplified stripe scheme is very easy to decal. The earlier full striping scheme will need some patience since there are a lot of stripes.