Welcome to EP.
GPIB, eh? GPIB is a rather old and no longer very commonly used interface. Superseeded by USB or Ethernet.
Anyway. What I find is heaps of utilities (hardware and software) to connect a PC or microcontroller to a vintage GPIB based instrument. I haven't been able to locate the same in the reverse direction (aka build you own GPIB based device).
Therefore the easisest way is to stick with your existing GPIB based instrument.
Another solution would use a virtual GPIB instreument (a piece of software) that translates GPIB commands to e.g. USB based commands for a modern instrument. Follow
this link.
The most inexpensive solution (in my opinion) is to use an inexpensice multimeter with USB (or RS232) interface and re-writethe software to deal with this instrument.
I understand that this answer is not exactly what you're looking for. I'm afraid there is no miniature solution available - as far as I know.