I would double check your pontoon brand. If you got it at Costco, then it is an Outfitter 300, not an Outcast. I don't recall Outcast making a 300 model but if they did, I would contact Outcast directly about a replacement shell.
If you have an Outfitter 300, I think that that boat may have been made for Costco by Classic Accessories in Kent, WA. Again, I would contact them directly for replacement parts. If it was a private label job for Costco, there is probably less chance they have replacement parts unless it was just one of their regular models re-branded for Costco.
In either case, your problem can probably be fixed by anyone with an industrial sewing machine. I'd try a tent/awning place or an auto/boat upholstery shop; either should have the expertise and some kind of material to patch it or re-sew a seam. However, if the cloth fabric on top itself ripped (assuming you have an Outfitter 300), I'd check all the fabric to be sure it is not starting to sun rot. (if you're not sure, ask the opinion of one of the above type of repair shops) If it is starting to rot, I wouldn't spend to much money on it or trust my life to it. If the fabric looks ok or it was a seam failure, you can prolong the life of the shell by treating it regularly with '303' and storing it out of the sun. If it was a seam that failed because the thread rotted, you can prolong the thread life by treating it with SeamGrip (being careful not to glue the bladder to the shell or the shell to itself).
Good luck!
If you have an Outfitter 300, I think that that boat may have been made for Costco by Classic Accessories in Kent, WA. Again, I would contact them directly for replacement parts. If it was a private label job for Costco, there is probably less chance they have replacement parts unless it was just one of their regular models re-branded for Costco.
In either case, your problem can probably be fixed by anyone with an industrial sewing machine. I'd try a tent/awning place or an auto/boat upholstery shop; either should have the expertise and some kind of material to patch it or re-sew a seam. However, if the cloth fabric on top itself ripped (assuming you have an Outfitter 300), I'd check all the fabric to be sure it is not starting to sun rot. (if you're not sure, ask the opinion of one of the above type of repair shops) If it is starting to rot, I wouldn't spend to much money on it or trust my life to it. If the fabric looks ok or it was a seam failure, you can prolong the life of the shell by treating it regularly with '303' and storing it out of the sun. If it was a seam that failed because the thread rotted, you can prolong the thread life by treating it with SeamGrip (being careful not to glue the bladder to the shell or the shell to itself).
Good luck!