They still make them. I recently saw them at Wal-Mart or Target. They do have their own web site, I am sure you can order from there. Also, Ebay would probably have them.
There are some shrinky dink supplies still being sold, mostly online. You can purchase the pre designed types where shapes are already drawn and can be colored or there are "books" of the plastic where a child can draw their own design to be cooked and shrunken.
