What a great recollection David!
Tunnel diodes were used in several Tektronix fast pulse generators, and in the trigger circuits of 'scopes and plugins. Anyone who has tried to get reliable triggering on a 7T11 sampling timebase will know how twitchy these can be. Before the fastest TD in a 7T11 went obsolete, Tek was charging USD800 for that TD.
Leo Esaki won the 1973 Nobel prize (with Ivar Giaever and Brian Josephson) for electron tunnelling. For a while it was known as the Esaki Diode, before Tunnel Diode stuck.
In a sense it is rather sad that they went obsolete not long after he won the Nobel.
If fast rise pulse generators are your bag, Leo Bodnar sells 30-40ps rise time pulsers for £50 to £100 (depending on connector). You set the pulse amplitude via the USB connection from which they derive power. They even come with a calibration certificate,
http://www.leobodnar.com/shop/index....ndex&cPath=124 .
I have one of his BNC ones, since most gear that I use uses a BNC.
Craig