I have a couple of Pimoroni Tiny2350's so I wanted a custom breadboard for it, they are so small it was a no-brainer. So, dug out an old breadboard, pulled out a couple of the tracks to see how they went together, googled the pin pitch of a standard breadboard (2.54mm) and cracked open Onshape.
This is the result.
So, this fits the breadboard tracks from that old breadboard, your mileage may vary. A Tiny2350 fits into it and the tracks are then soldered onto the castelation points on the Tiny2350.
There are 32 tracks, 8 per side for the Tiny2350, so 16 there and a further 16 below those.
Onshape: https://cad.onshape.com/documents/91f2d1d81e4863c294a2573b/w/6ff524a4ce11ca29fc5b10b5/e/5503f8b060f5a412d114cf87?renderMode=0&uiState=66e5a3fe495df232ce8eb13f
Printables: TBC