I actually used a flexible dewshield from my little Celestron telescope. I had to wrap it around a couple times and secured it with some velcro. You can also make one from black heavy duty construction paper and tape. It's a simple device you can make for cheap.
I do have a question about the length of the snoot. I assume the longer the snoot, the narrower the beam? How narrow should you go? I suppose it depends on the effect you desire.