I’m looking for a socket that will allow me to easily switch out to-126 transistors for matching.
DIP sockets. It’s the right spacing, and you can blot both to a little piece of aluminum in between to keep them at the same temperature.
The lead spacing is .100 inch or 2.25mm. you could use an IC socket depending on your current.
https://www.farnell.com/datasheets/43624.pdf
https://www.farnell.com/datasheets/43624.pdf