I've never seen one for sale before.
For you young types: this is what Germany used in WW2 for secure communications. Except that the Poles & British had broken it and read everything. Britan then gave it to its own diplomats and Commonwealth countries to use after WW2, without ever disclosing that the codes were broken. So England could still read the letters...long before PGP & Entrust were developed.
It's currently going for $32,000 USD with a few days to go.