The OP is over the water in the USA. Any auto paint specialist worth their salt will have a spectrograph that will allow them to produce a colour match from a sample. However, as mentioned by the previous poster, this does not come cheap. Usually these paint Specialists can provide this matched paint in a number of forms - 1 pack and 2 pack a acrylic or cellulose, either premixed for spraying, in a rattle can or unthinned in a tin. They might even be able to provide it as a touch up stick.
Personally I would strip the loco down to component form. "Annies" are fairly simple, and if you no longer have it, the assemblies sheet should be available on the Bachmann site, to aid you. Prep it properly, light abrading of the surfaces so the paint has something to key onto, primer coat and then effect a full respray in the colour that best suits your needs. Finish with the laquercoat of choice. The same auto paint specialist shoul be able to provide you with all the paints ready mixed in cans that are all cross compatible with what was thre to start with and what you bought. Max