A Walthers search wouldn't help much in this case, because most of the models are/were/will be from Athearn, whose products Walthers doesn't carry.
A search for NdeM at
www.athearn.com yields one or two out-of-production GP38's, and two improved GP38-2's expected early in January, plus Genesis F9's coming both with and without sound. Also a bunch of freight cars, most "temporarily out of production" but probably on some dealers' shelves. The freight cars wear the fairly old (into the 1960's?) livery; the one with the more recent billboard italic initials, the "ACF 50' boxcar", isn't shown with a picture.
In addition to the models listed at its current website, Athearn also had a Special Edition three-pack of two kinds of cabeese decorated for the NdeM.
There was also a producer named, I think, Mexicano Models, that decorated Athearn freight cars for Mexican lines, probably including the NdeM. I have an orange Chihuahua al Pacifico 50' boxcar with a full color picture of a Tupamara Indian running; I bought it used, without a box, but it probably came from that line.
