You could put a wanted ad on here. May get a second hand set. I'm not sure how close to the intended spring rate they'd be after 25 years but could be a choice if you're struggling to get originals. Another consideration would be to talk to eibach, koni, etc who all manufacture OEM stuff. One of them may have been the OEM supplier at one point or another.
I understand the whole wanting it to be as the brochure said but working in the automotive industry I can confirm parts get changed constantly and aren't always reflected in the brochure, so it's not the end of the world if originals aren't in existence anymore as...... well, it's just a spring with a set rate on it basically!