Manufacturing for cloth material + seed-based "warming bags"

I am contacting this site in behalf of a customer i am working with. I am looking to facilitate a manufacturer agreement for my customer, such that hey would not need create the product they are selling themselves anymore. My customer is producing hand-stitched cloth bags/puches with various types of seeds (flax, barley) filled in them. These serve as "warming pouches", which a customer can put into a microwave to heat up. Its a great product for relaxation, warmth and general body pains. The requirement would be that it supports the use of various types of fabric patterns to produce the pouches, the pouches may come in a variety of sizes, and must support different type of seed-based fillings.