The answer to the "why doesn't he sell them" question is, I believe, that someone was killed many years ago in one of his designs, and he felt so bad that he decided never to let them, or the design, onto the public market lest he be made to feel responsible for more deaths. Sad, but understandable.
And I too once wrote to him - must have been 35 years ago, and received a lengthy and very informative reply from him.
Wonderful man.