Hi,
I believe that the GPIB driver for 3.1 came with LabVIEW itself. It is hard to find any information on it as LabVIEW 3 is very old. I am sure that you saw this site, but check ftp.ni.com/support/gpib/mac/driver/archives/ for more intormation. I do not have a mac here so I cannot see what installs with what. But again I would suggest looking on the LabVIEW (CD? Disks?) for the driver itself.
Hope this helps out!
Best Regards,
Aaron K.
Application Engineer
National Instruments