ASTATIC D-104 ( D in this case means dead)

[KD8DEY]

Yup, The Commentator 10_DA 50hz-10Khz.
You can still catch them on Flea-Bay, Along with the Kobetone replacement D-104 elements.

I've got one of those ole bullet heads sitting in a drawer waiting for me to find a stand for it
(Moneys short).......Eventually want to find a t-up9 with the original amplifier board (Not the newer/last version)

[W7GIF]

The usual problem with crystal microphones is the absorption of humidity by the Rochelle salt crystal. Even in a relatively well controlled atmosphere it happens eventually: sometimes a gentle baking in the oven at about 40 to 50 degrees Centigrade would restore them.

Peter,
Thanks for the info regarding possible resurrection of the D-104's by "baking". Unfortunately, it didn't bring my mics back to life. But, thanks for the suggestion, nonetheless. 73's......

[W8XLR]

These work GREAT, I have several...

http://www.rbmicro.com/index.php

[W9GB]

RB MICRO is back ordered on replacement mic elements.

You CAN grow your own Rochelle salt crystals  (K·Na·C4H4O6·4H2O).
That is how Astatic did it !!
http://www.homepages.ucl.ac.uk/~ucfbanf/general/crystal.htm

High School Science Fair project
http://www.seawhy.com/xlroch.html

http://chemistry.about.com/od/crystalrecipes/a/Rochelle-Salt-Crystals.htm

http://www.mo-seph.com/node/489

Canadian secondary schools had a contest in 2000 ... Impressive results.
http://home.nas.net/~dbc/cic_hamilton/crys.html

There is a YouTube video, time lapse for the 12 hour growth process !

==
With all of the illegal street drug labs, you should be able to find a local chemist.