You can almost assuredly find agar and xanthan gum at natural food stores. Carrageenan is harder to come by, but you may find it at well-stocked natural food stores or home-brewing supply shops. Note that carrageenan may be labeled “Irish moss powder.” Of course, you can easily order all three online. Here are some websites where they are available:
- amazon.com. A good source for agar, carrageenan, xanthan gum, and just about any other nonperishable ingredient you can’t find locally.
- barryfarm.com. Agar powder and xanthan gum.
- bulkfoods.com. Agar, xanthan gum, tapioca flour, arrowroot powder, and many other natural foods in bulk.
- iherb.com. Agar powder and xanthan gum.
- lepicerie.com. Agar, carrageenan, xanthan gum, and other hard-to-find ingredients, and also high-quality chocolate, flavoring extracts, exotic condiments and spices, and more.
- modernistpantry.com. A good source for carrageenan in reasonable quantities.