The 3 series boxes are now better supported for a variety of reasons. First, a rise in interest in preserving the ordinary cars they came in (R16, R12, R17, etc). Second, the fact they were used in very desirable specialty cars, notably Alpine A110 and A310. Lastly, the same interest is only just starting for Fuegos et al. People switched to NG3s because of the enormous reserve of scrap vehicles and, at the time, continued factory parts supply. Both of those have timed out now. It is getting very hard to find Fuegos now. Barely a blip on the production map when new, Europas easily out number them now.
That all said, the person quoted may not be familiar with the Lotus-Renault 365 with its Hewland supplied 0.85 5th gear. Spares are rapidly approaching pure unobtainium and was the reason for Banks to start the shift to NG3s in the first place.
My transaxle project was delayed a year but I will probably have a few rare 365 spares available when it is completed: ring and pinion set, excellent 5th gear set, rear housing, and a NOS 5th shift hub assembly.