I got a couple blanks of that blue water ribbon acrylic and tried a whistle from it. I'm digging it. Building see-through whistles is a nightmare, but it came out pretty clean.
I've seen this stuff a number of times but nobody will say where they get it, even when asked. So I apologize (not really) ahead of time to anyone and everyone that may take offense to me divulging the source, but this is THO and nothing irks me more than crickets when people ask where to get a material. Not to mention, the service from this guy was awesome and he has a huge selection of really cool poured blanks.
http://www.beartoothwoods.com/catalog/index.php?cPath=99_77 All sarcasm aside, I do apologize for buying the last of his blue ribbon blanks.
I want to get my hands on some of the orange ribbon blanks, as they look really cool. Backordered....