I had a similar issue with my old 4x4 a while back. I found that eBay and Amazon were great for finding diagnostic scanners for older models like the 1993 Samurai. For the map sensor, I had some luck with local auto parts shops—they might be able to order it for you or help you track one down. Sometimes, specialty forums or Facebook groups dedicated to off-road vehicles can be gold mines for finding rare parts too.
For a diagnostic scanner, look into scanners like the OBD-I code reader or the Actron CP9175, which are designed for older vehicles like your Samurai Jimmy.