Hello, and thank you for your inquiry regarding a source of mined gypsum for organic ntfp production. A good place to look for suppliers of inputs that are suitable for organic operations is the Organic Materials Review Institute (www.omri.org). They have an online searchable products database; I typed in gypsum and received 38 results:
If you are a certified organic operation: It is always important to check with your certifying agent before buying or using inputs just to be sure there are no emerging issues with a product or a supplier, and it is necessary to list all inputs on your Organic System Plan.
For more background on suitable inputs, see the following eXtension article: "Can I Use This Input on My Organic Farm?"