Josephine Porter Institute, known as JPI, in Virginia. I have been using them for years and they are top quality and good price.
If you are just starting with Biodynamics, I reccomend using the Pfeifer Field Spray for the first few years, especially on your garden and orchard. It contains all the preps and is straightforward to apply.
The Pfeifer Compost Starter is excellent for innoculating your compost pile, easier to get good results with than the Set of Compost Preps.
The Compost Preps are the real deal, but only reccomended if you are already good at making finished compost.
Feel free to ask any questions as you begin the path to Biodynamic farming.