Not that I can really think of.
Any bits of Styrofoam, carved to shape, and then coated in a wood putty, or a mix of white glue and water to add strength to them should do.
Mount on thin sheeting, made of styrene (for sale signs, etc., sold at the Dollar, or home improvement stores will work and are cheaper than buying at the hobby shop), thin metal bases, or the new material recommended, that I haven't tried, e.g. vinyl tiles should work. The latter can easily be cut to shape with scissors, I've read.
Use white, or other glues to attach to the bases.
Then paint, flock, seal, as desired.
Water-based paints (acrylics) for painting the Styrofoam are required.
You can also make small berms, positions, etc. out of air-drying modeling clay too.
