As no RTR model has ever been released and with only 46 ever made perhaps never will.
They may have been made in brass?
I think a kitbash/scratchbuild will be required in any scale.
Being as this diesel has been described as two Baldwin DS4-4-1000's on a common frame;
and Stewart (in HO Scale), have released a DS-4-4-1000, then a couple of these shells and
a custom built frame with trucks from a Stewart AS-616 perhaps might be a starting point.
Microscale has a decal set 87-992 for Confederate Gray and Epaulet Yellow FT units, which may be usable for the as delivered paint scheme.
( I did use their Daylight set for F units 87-50 on a GP7... )
There were two orange and black schemes, the early 1951 one had an orange arc on the cab the latter 1955 didn't.
Both should be a fairly simple mask and paint using Daylight orange and black with 10" Cotton Belt decals from Microscale 87-11.
The scarlet and gray scheme applied in 1958 followed the previous paint mask, and is different to an SP standard, decals would be the same as above.
- Extra 2200 South, Feb 1969 page 18 - photo of early orange and black scheme
- Extra 2200 South, Apr 1969 page 21 - photo of early orange and black scheme
- Cotton Belt Locomotives by Joe Strapac - page 194/195 for as delivered paint scheme and scarlet and gray scheme
- Cotton Belt Pictorial by Steve Allen Goens - pages 54/55 color photos of later orange and black paint scheme