The GA ones (12-car) don't exist, then!
Er, they do. What Stadler did was to effectively build two coupled 6-car half-units to make up each 12-car set (a bit like the original Eurostars), but with a cab at only one end. I forget if they have both pantographs up, but a bus-line down the roof is hardly a difficult job.
They are 236.6m long, so if you wanted 250m you could add one more vehicle, or two if preferred to keep the half sets the same length.
If there's the money, a way can always be found
This photo (from Railcolor News) is of the two "end coaches" in the middle of the formation, they aren't articulated and have all the electrical gubbins but no actual cab: