I'm sure you can retrofit them. I believe most manufacturers use Flexsteel. Here's a link to their RV sectionals:
http://www.flexsteel.com/vehicle-seating/products/motor-home-seating/extenda-flex-lounges.
It looks like you can order Flexsteel sofas through CampingWorld. Their website doesn't list the sectionals but I'd be very surprised if they couldn't order it. One issue is that I think they are fairly expensive - I didn't see prices anywhere but I'd be surprised if they were less than $3k.