How to connect to tiny pogo pins in test fixture?
Pogo pins are designed to be placed in pogo pin receptacles or sockets, slightly larger sleeves made of similar material.

Your P50 pogos would use an R50 socket, P75's would use an R75 and so on.  Knowing that will drastically improve your chances of finding an online vendor.

Common socket forms have an indented rear to which fine wire can be soldered and covered with tiny heatshrink after the socket is pressed into a CNC drill hole in a carrier plate.  You can also sometimes see them sold with wires already attached, which saves some fiddly handwork.

At least in the R75 size in addition to the solder form (such as R75-3S), you can get sockets ending in a square header pin (R75-2W) which you could wire wrap to, or possibly even use a socket jumper wire, or if you match a standard header IDC ribbon cable connector on.

In a pinch you can carefully solder to the pogo itself; the downside is that if it wears out, bends, or start sticking in use, you then have to replace the wiring too.  In contrast, if sockets are used you just carefully extract the bad pogo with pliers and put in a new one.