Declassified NSA documents describe some of the systems.[1] Early systems used paper tapes for the key. One of the features was a tape slitter, so the tape could only be used one time before it was cut in half. Systems with floppy disks have been advertised. Mils Electronik sold one time key systems from the 1950s until 2017.[2] Early systems used paper tape, later systems were electronic and stored the keying material on PCMCIA cards.

[1] https://www.nsa.gov/portals/75/documents/news-features/decla...

[2] https://cryptomuseum.com/manuf/mils/index.htm