I've an HP 8558B Spectrum Analyser with dud diodes in its first mixer (one
shows 0.33v forward, high resistance reverse, the other 11 ohms either way
around)

The official part 08558-20095 and its replacement 08558-60152 have long
become obsolete. Can anyone suggest a substitute? The application is in a
low power balanced mixer mixing input signals in the range 0 to 1500MHz with
a Local Oscillator tuning from 2050MHz to 3550MHz to produce a signal
passing through a 5000MHz low-pass filter to a 2050MHz bandpass filter. The
present diodes are small glass wire-ended diodes about 4mm long and about
1mm diameter.

Many thanks in advance.

John