I doubt you will find a replacement for the CR69 tunnel diode unless you can find some old stock. They are a low capacitance (0.5pf?) 50 mA tunnel diode in a tiny pill capsule to get the very fast switching time. There are a number of varieties of TD from Russia but I don't know of any such high speed switching types or in that package. The fastest I've found is 20 mA and a few pf in a 3 mm pill (different to the Tektronix shape), I don't think it would be as fast even if the circuit values were altered to drive it. Hope you can find some spares.

Don Black.
PS if you try and get some of the Russian diodes, the same type has wildly different characteristics depending on the last letter so check the details carefully. They seem to use the same photo for the varieties so don't rely on the numbers on the packet pictures. The Russians seem to give good service.