Or did you e-mail them? Mardi almost always answers the phone (1-800-257-8192) and always willing to help. Fat shafts are probably out the question but standard 1-3/16" shafts should still be available. You might contact the OEM manufacturer too (GKN Driveline)
No new half shafts are available to my knowledge. RAxles got shut off from their supply of OEM CV Joints. Ford no longer makes new shafts but you can get remanned units. The problem there is no one lists Fat Shafts or shows any difference between the SC versions vs. the conventional half shafts. Unless you can find someone to rebuild the exact units you send them you are pretty much assured not to get back what you send in as a core. Could check with RAxles to see if their situation has changed but I would not be holding your breath.