Oldest gear still for sale is . . .

I wish we could say the Shure V series. They should never have stopped making it, even if they had to change the cantilever. 

Does anyone know when Jelco started selling the SA-250ST? It had to be in the 1980's, right?

I personally am using a Stax SR5-SDR6 electrostatic headphone system, McIntosh MR74 tuner, and a Yamaha CA800 integrated amplifier on a third, small adio system.  What all there of these have in common, besides all of them at least 35-40 years old is that they are still incredible.  Trully, totally.  So much of this "old" stuff is still in excellent condition.  Used with todays latest power cords, power conditioners, interconnects, speaker wires, etc., some of these "ancient" audio products are definitly not out of place today.  I can still remember 40 years ago the Yamaha CA1000 integrated amplifier was being praised for it's preamplifier and matching phono preamplifier attributes.  And, in fact, my present Yamaha CA800 integrated would be hard pressed to be equalled today for less than say $2-$3000.  My Stax headphone system, for which I paid $100, sounded very like a $2000 Audieze pair of headphones I once heard.  And my MacIntosh MR74 tuner-well I recently sold my Day/Sequerra as it was nowere being it's equal.  No, for the money, carefully selected "old" stuff can be hard tobeat.  And lots of this can be found in basicsally mint condition.  And, of course, old timers such as myself are dying right and left  all over the place.  So the current situation should continue for some time.  And their prices are sure to be going up as more of us realize what treasures are outtheir for the picking.

Not many components can say they have been in commerce for a long time, but haven't become dated and superseded by more current gear,

The SME V arm came out in 1985, was considered one of the handful of top tonearms available, and continues now, 32 years later in the same company.  Hard to think of any other component that has not only continued in production but has also held its place vis a vis newer gear.