In fact, I believe that he has. Like much of the Origami community, Michael is very generous, even though he has to make a living. If you look in the front part of Advanced Origami, there's a detailed discussion about paper making. In addition, His Frog CD spends nearly half of the CD talking about making Frog paper.
The recipe is not the 'issue'. The time, patience, technique, and equipment are the issue. However, you can go to his shop and he used to have workshops etc., for making the paper. I believe that Robert Lang buys special batches of paper, and Satoshi Kamiya was famous for spending time (weeks, months?) with Michael learning how to make paper. Phoning Origamido for paper used to be the cheapest way to buy it. (???)
My point is that if you have the time, patience, and money for resources, you could probably learn how to make your own Origamido paper. As far as I know, Michael and Richard used to make batches of paper for their own use, then sell any remainder. I don't think they make much of a profit, if any, in the process ... but I don't think they made the paper for general sales, selling excess mostly as "a favor' to the Origami community.
[Michael, I'm still waiting for my promised kickback sample papers

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