Have you checked out the FAQ's yet? I just use some 1/4 strgenth Fox Farm, Grow Big to get the seedlings off to a good start. This product is available at the stores you have access to.
http://www.terracycle.net/
I just noticed that there site is down. Here is another link to the product, I have seen it at The Home Depot.
http://www.cleanairgardening.com/terracycle.html