gg, This is where I get mine.
The company is a delight to deal with being friendly , helpful and providing fast service.

http://www.concretedepot.net/catalog/index.php?cPath=115

You can get a few 1 pound bags for the same S&H charges (ask them).

Unless you are going into production I think one or two bags will last you forever Since the avg project only needs a large pinch full.

Thanks scooterbug. That was quick and it looks like it is just what I need.

I find 'em at the local masonry supply store.