Most of the old type phones used a carbon mouthpiece element and a crystal earpiece. The crystal earpieces have two screws. Screw the ground to one and the center hot wire to the other and you have your Mr. Microphone.

eBay is the best place to watch for the old crystal mics from the 60's. Usually really cheap. Under 15 bucks.

I still need to solder this thing together so I can actually use it.

_________________
Favorite bands:

Melvins
The Jesus Lizard
Cows
Big Business
R***man
Minutemen
Flight
Minor Threat
Big Black
Shellac
Karp
Scratch Acid
Wipers
Pixies

The only 2 are both over $100

_________________
Favorite bands:

Melvins
The Jesus Lizard
Cows
Big Business
R***man
Minutemen
Flight
Minor Threat
Big Black
Shellac
Karp
Scratch Acid
Wipers
Pixies

Just keep watching. Some will popup. You are probably seeing com microphones and yes the vintage com mics are pricey. I've seen them with some old tape recorders at a couple of "antique" shops around here for like $20 including the recorder.