I can't help much with replacements, but I've been fighting dying rear wiper motors on one vehicle or another for years, and I will put in a couple of suggestions here for those who have not yet lost theirs.
First, if you make the mistake of turning on a rear wiper that is frozen to the window, or freezes before it finishes wiping, do not just turn it off. Turn off the ignition and free it with ignition off. The park circuit of the motor may burn it out if you leave the ignition on. Sometimes they do not burn out, but strip the gears instead. Either way, you're done for if that happens.
Most rear wipers bind because the shaft corrodes. If yours is slowing down, get out and help it get back to the park position before it burns out. If it's still working intermittently, you might be able to free it up by helping it along for a few cycles, though it will stiffen up again soon. Best to get it parked, then leave it off until you fix it. On older ones, you can take the motor apart and lubricate the shaft. Just pull it out, clean it up, grease and reinstall. Newer ones are riveted together, but you can still drill or mill the rivet heads off, take the motor apart, then use little screws and nuts to put it back together. A drill press and an end mill will do the job nicely if you're careful. A Dremel tool will do it too with some patience. Given the price of a good new one, it's worthwhile to fix a dying old one before it quits. You might be able to work a little lubricant down the shaft from the outside, but it's better to take it apart, because the shaft is very long and corrodes quite deep in.