I lot of these are too fine to be able to mask (in N scale). If produced by model companies this could be easily done with Tampo printing, or even ink-jet (like the one MT used to decorate their recent releases). A method I'm not a fan off because of the relatively low-res and very visible surface texture.
For individual modeler, custom-printed decal would probably be the best way to go. Get yourself an Alps printer (while they are still few old ones kicking around) and start making your own artwork.
