I finally got this out by removing the hardware with the door in place. It took several hours of finagling.
Even with the hardware removed, the door itself cannot be removed from the pocket. There isn't enough clearance to bend it around the corner in either direction. Seems I may have to mount the replacement hardware using the same torturous process in reverse.
Also, unfortunately the track is mounted to the trailer frame inside the pocket with wood screws that are far out of reach -- so removing the track is also not an option.
When I remount the new hardware, I'll be sure to mount the rear slider closer to the opening so it is easier to access in case this happens again. What a pain!
By the way, the closest I've come to a replacement roller so far is here:
Amazon.com: Slide-Co 162168 Pocket Door Top Roller Assembly with 7/8-Inch Nylon Wheel: Home Improvement
The wheels are the correct size, and the design is similar, although not the same. No way to know if it'll work until I try it.
I haven't checked with Inland yet. Vintage Trailer Supply doesn't seem to have anything. If anyone comes across a better replacement, would love to hear about it.