Where to find a Shure 401 B?

Hi guys, I'm new here! I'm a microphone enthusiast and I found a Shure brothers 401 B plunger style push to talk intercom mic. I can not seem to find any sellers of this old fella out there. Do yall have any tips or tricks on places to search on the internet for such odd rarities like these? I know about reverb, ebay, etc. But I wondered if yall might have a few other options more specific to microphones.

Thanks for the help!

Here's the mic