I once almost ordered this which may be of interest to you. But I didn't actually get it, so can't offer any feedback.
I've had good experiences with the folks at SulcataFood. They sell a grass seed mix and a number of other plants. The site I've seen recommended a lot on this forum (for the whopping 1 month I've been a member) is TortoiseSupply.
Just a reminder to watch out for buying plants from stores if you don't know what the plant/soil was treated with before you got there. Stores like Home Depot and Lowes sell cacti for ornamental purposes, not pet consumption.
Whether it's wheat grass or something else, once you know what you want, consider finding a local gardening store. They're generally cheaper than pet stores, and they'll be able to tell you which items of theirs have been treated with what. Even if they don't have what you're looking for, they may be the best people for pointing you in the right direction. Also, if you're looking to buy grass seed, they may sell it by the pound, which means you can get exactly however much you need.
Here is some organic wheat grass and a couple others that I ordered on Amazon this last Autumn. All seeds have germinated PERFECTLY. I've had great crops all winter. I HIGHLY recommend ordering these...
Barley http://www.amazon.com/gp/product/B001156C5K/?tag=exoticpetnetw-20
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I've been having a ton of fun researching and trying out what foods I can grow for indoor and outdoor Sulcatas. Here are a few ideas and I'll give you a couple links on the forum to check out: Squash Vines (pumpkin, zucchini etc) are good sulcata food, weeds and flowers in the Mallow/Alcea family are good like the weed "Mallow" and flower Hollyhocks, Hibiscus, Dandelions, Plantain, clover, Mulberry trees,& Grape vines (avoid letting sulcatas eat fruit).