Gene,
You will need to scratch built your "crib" retaining walls. There is nothing out there that I can find in N scale that resembles a log retaining wall. I assume that you are talking about the rock retining walls on top of tunnel portals. These are called "cribs" and were put in place to hold back loose rock that might fall on to the tracks from above tunnel excavations. They are composed of vertical and horizontal log pieces, sometimes with wire in the open spaces, to stop the rock. If you are talking about vertical retaining walls at the side of tunel portals like wing walls, Campbell makes these in conjunction with their wood framed tunnel portals. Other than that, just plain retaining walls would not usually be made of wood. So, again, I am trying to provide information without having all the facts.
B-)
