Updated 3/9/10: The document he gave all the kids is here: gyotaku.
There are also an out of print book for sale at Amazon — Gyotaku: The Art and Technique of the Japanese Fish Print
The Art Store (website here) in Windsor Heights/Des Moines has printmaking supplies.
If you don’t have real fish, you can use replicas.
Or a 9-piece set is available: Gyotaku Fish Printing Replicas – 9-Piece Fish Set
We’ve also found a DVD: Art In The Classroom Series: Gyotaku
A nature print book that is kid-friendly: Nature Printing: 30 Projects for Creating Beautiful Prints, Wearables, and Home Furnishings