Well, it's not a canned product, it would be one that you would roll yourself. Basically, I'd be dropping in a choke and a cap to ground to stop any high frequency from making it onto the tracks. Since you're running strictly conventional, you can make the filter fairly aggressive and kill anything above a few khz.
For the transformer feeds, perhaps this 9A 47uH Inductor in series with the leads with a .1 uf capacitor across the track side. For the locomotives, I'd put one of these 3A 33uH Inductors in series with the hot lead with a .1uf capacitor to the frame.
Do that to one transformer and one locomotive and see if you get positive results.
