Alfalfa is offered in local feed stores in a "pellet" form, (Compressed, dried) I took a handful and put it in my coffee grinder, to make it a fine powder. If you don't want to buy such a big (40Lbs) bag, I am sure you can order from Amazon, or get a small bag of Alfalfa from a pet store, which offers items for Rabbits.
p.s. Kelp, and Alfalfa are good for you too! Sprinkle over your own food!! Here some info about valuable herbs for dogs and people:http://www.dogsnaturallymagazine.com/nutritional-herbs-your-dog/