Why is the 4 wire resistance measurement important? And what kind of accuracy is required?
There is not much sense in throwing old boat anchors at the OP without this information. For example: there are cheap LCR meters out there (less then $100 new from Ebay) which do a really fine job measuring resistances in the tens of milli-Ohm range with 0.5% accuracy.
Those old 56(a's?, the rack-mount ones) were tanks. It's not like he's out there advocating tube Knight VTVM's or Heathkit scopes from the 50s. Those are still decent bits of kit today.
Where can you get LCR meters for 100$ new (other than those all in one chinese bare-boards all in one testers)? I'd rather pay a few (hundred) dollars extra for a company I can complain to.