TstebinsB,
"shell" is another word for "leather taken from the butt of an animal" so the hand american strips are shell strips. Or try Tandy:
http://www.tandyleatherfactory.com/p...number=4578-00 This is the strip that I used (it's actually less than 3", like 2.5", I find it to be the perfect size anyway), but I have a store in town, so I didn't order it. I remember it being a little more expensive, maybe it was a longer strip. Oh well.
Here are a few other options if you want latigo or a different size:
http://www.tandyleatherfactory.com/products.asp?dept=23