This is going to sound really, really stupid...
I was presented with this problem recently myself. I planned on using Woodland Scenics snow, but the LHS was out and I couldn't wait. I was at the local art store and they had this big bags of white, semi-transparent (very semi) white tiles for $2. Then the wheels started churning. I bought the bag, broke a number of tiles into little pieces then put them into my spice mill. They ground up into a fine, fine powder that shimmers. It's cool, though, I'm sure not good for the spice mill.
The ground glass was easy to apply. I coated the area I wanted snow on with Future, added the glass and then covered with a few layers of Future. It ended up looking pretty good.
Here is a pic:
~ g