Tektronix TM Series Test Equipment?

[Neomys Sapiens]

Got it... sorry for the confusion.  There's a guy on the TM500 groups.io list that has a pretty nice extender kit. Not terribly expensive. I don't know if he is still making them, though. Anyone want me to send him and email and find out?

I snagged an original Tek extender, so this is not my problem. And I would ask Texaspyro first, as his is also good for the TM5000. I am looking for proto boards rather for experimental and build-to-purpose usage.

[Neomys Sapiens]

UPDATE!
I just bought TM500/TM5000 proto boards from a seller on Ebay Kleinanzeigen.
Multiple Boards available! I paid 52.- for two boards. Known persons from US/UK can be helped.
The boards in ENIG (Electroless Nickel Immersion Gold) technology even have labeled terminal areas for TM500 (front) and TM5000 (rear) contact allocations. Size is 229mm * 113mm.

See also here:
https://www.eevblog.com/forum/testgear/test-equipment-anonymous-(tea)-group-therapy-thread/msg3819899/#msg3819899