I considered mentioning the sliding/reclining seat as a caveat but assumed so few people specced it that it would be a moot point.
Dealers in general tend to shy away from anything off-spec, even if it was actually available as an option, which is why I can't get the sliding/reclining rears (dealers in Turkey refuse to even order it as the part number is not associated with the VIN, let alone fit it). The floor rails are the same as the standard seat, so if you were to order it, it would take an afternoon and 12 bolts to fit yourself, provided you don't have any back health issues. The electrics (seat sensor, airbag and heated seat - if specced - wiring harnesses are plug and play, and the body computer doesn't cause a fuss unless you're moving from standard to heated seats).
Getting back to the original point, since you have the reclining rear seat, one of the best things you might want to do if you get the folding passenger seat is to find a pillow of sorts that will raise your waistline to a flat level to the folded passenger seat. It folds up and sets up very slightly higher than the height of the rear bench. At first sit, having your feet up feels great. After you nod off, you wake up with numb legs. Removing the plastic 'picnic table' seatback might help and make things level, but it's not upholstered like the standard seat and getting it off is a hassle, not to mention it exposes the headrest anti-whiplash mechanism once off.
As for sourcing, a breaker yard might have one for much less than a new one from the dealer.