SR (Sakae Ringyo) is still around. In fact, it bought the defunct SunTour name and now markets products under the "SR-SunTour" moniker.
Other extinct companies include Weyless, Hi-E, Arnold Industries, Artisan Tool & Die (still around, just not making bike tools anymore), Edco, a whole slew of French companies including Simplex, MAFAC, CLB, Belleri, Huret (bought by Sachs, then allowed to die, as were Maillard and Sedis), Super Champion, in Britain Williams, TDC (still around, just , not making bike components anymore), Belleri, etc.