Got two leads for you. The "G" sensor is apparently also known as a "Road" sensor and was on US Troopers in the 94-96 time range. The first link is to the OEM Parts Catalog on IsuzuParts.com. Set your vehicle to be a 94 Trooper and keyword search for "sensor." You should see G-sensor somewhere on that list. The second link is to a former Isuzu dealership in Florida that has a bunch of parts they're trying to get rid of on the cheap. Not sure if they still have it in stock, but if they do, it's more than $100 less. Here you go:
https://www.isuzuparts.com/catalogs.html
http://www.leeautomotive.com/isuzu-p...learance-page/