Yeah, looks like top shelf stuff. Here is another good one, and you can get it in only 4oz. amounts.
www.delviesplastics.com
They even have some that are UV reactive.
A little higher priced than Ben's source, but not to bad, and quality is top shelf.
And a interesting selection of plexi as well. Do wish the carried Polycarb though.
Lexan and also carrys adhisives:
www.mcmaster.com
Have you completed your tower res yet? Results? Pics? A good idea and design, still like the way you used it to greatly shorten your lines.