You can google
cat grass

There are plenty of hits, many with seeds.

Whenever MY cats eat grass, they later vomit it up. NOT something I want to encourage by growing it!

I've had some success using Barley Cat. It is a green powder supplement you sprinkle on their food. Helps give them what they are seeking by eating the plants. Here is just one link (search for a good price, but this lets you see the product)
http://www.vitacost.com/Green-Foods-Barley-Cat

With 10 cats in the house (down from 11), I just gave up on house plants.