I am looking too but have found it to be impossible to find one that will allow me to use the factory seat.
If using the factory seat, you will need a base from an early (75/76/etc) G series conversion van, hard to find. If you find one (or two) buy em both!
If you have aftermarket conversion van seats, there are lots of swivel pedestal options.
BTW, I'm glad to see you got some rear popouts.