I'm interested in this product myself but have never played with it. The stuff looks like it could be extremely useful for buidling cages and much cheap than acrylic of the same thickness.
Try http://www.usplastic.com, or if you're in/near Texas I know of a place in Dallas. The company name is at work, so email me if you're interested.
Check out these two web sites for possibly useful info:
http://www.bayplastics.co.uk/product guide/foamalite-guidelist/prod-formalite-guide.htm
http://www.solarbotics.net/starting/200207_sintra/200207_sintra.html
If you do use this stuff, please post your thoughts.