Western Depot has both Shadow Rail and Super Snap (compatible with Shadow Rail with a transition piece or just trim off the "ears."
Here's the link:
http://www.westerndepot.com/catalog/index.php?cPath=21_36&osCsid=a0b12918678781d964cd7363a2c626db
If I was you I would try Eastern Depot or Just Trains.
Alex
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