Answer: So many of the currently available shrubs and perennials have dwarf or compact growing habits, you shouldn't have any problems finding suitable plants for your railway garden. Mugho pines are slow growing, and can be pruned to keep them bushy and small in stature. Some of the smaller leafed groundcovers include Phlox subulata, creeping thyme, Soleirolia (Baby's Tears), Lysimachia nummularia, and creeping fig. Ornamental grasses might be a nice addition - blue fescue is a short, clumping variety.
Hope the above gives you a start on your list of plants. Many other suggestions can be found in Sunset Western Garden Book (ISBN# 0-376-03851-9).
Q&A Library Searching Tips