The back seat of an RV-8 is not a great spot for either instructor or student; limited control access and poor (if any) view of the instruments.
There isn't much in the way of tandem seat available in the certified world, mostly competition machinery such as Extra, Zlin or Pitts.
If you accept SBS seating, then a CAP would meet most of the other criteria - the 10C is still in production. YAK52s are plentiful, but the running costs are likely to be at least double.