Seems like everyone already suggested anything I thought of --
- feed supply stores
- Natural Balance LID (limited ingredient food) here is a link:
http://www.naturalbalanceinc.com/dog...as/SPFish.html

- Cooking or them, which you said you do already quite often. I recently found this book at my library, decided I liked it so I bought it:
The Whole Food Diet by Andi Brown

She includes recipes, and discusses which food / herb does what.

Good luck!