Both Inkpress and Red River have c2s media. For down and dirty, I use the c2s Epson matt though it's only 8.5 x 11. I use that for fold-over cards and simply use the rotatrim.
Now that I think of it, Averey did have a 2-up perferated postcard stock, but when I used it years ago, it was a calendared stock good for a laser printer.
Check some of the specialty paper vendors and you may get lucky.