The problem you will run into is that the original creator has not granted permission to copy or distribute, so anyone who reskinned it for you would have to start their image from scratch. That is almost impossible for that loco, as the whole image is in one file that is mapped to the mesh.
A much better option is to save your money for more important things and do it yourself, starting with the existing image and making small changes. Once you have a workflow set up, making and testing each change is easy. There is no need to use a complex high-end painting program, as most of what you are doing is copy and paste or built-in effects such as texturing or re-coloring. See, for instance:
https://en.wikibooks.org/wiki/Trainz/Tutorial_for_Reskinnng_a_Locomotive_using_Paint.Net