the PR4 you seek came in the 90-91 Integra LS and GS. You do NOT want the 92-93 PR4 that came in the 92-93 LS and GS integra.
The only reason why a PM6 chipped with PR4 fuel and ignition maps is superior to a PM6 is that the cars are electrically wired subly differently. The PR4 has an input for power steering control and a standalone AC/AC fan controller. The PM6 has an input for ELD, controls AC on its own. Very small subtle differences, but in certain situations important nonetheless.
If you can't find a PR4 on your own I have a couple sitting around.