I just went thru this. My fronts were about 2-3mm from squealing, but the rears have plenty of life on them, so I left them alone.
If I were you, I wouldn't confine my search for OEM discs. They are FoMoCo parts, and are probably seen on various iterations of Fords, Mazdas and Volvo FWD cars. The problem is, you really don't know who is forging the iron used to make the rotors. By now, OE could be from the lowest-bidder in some rinky-dink inland Chinese firm that puts out lousy, sub-par metal. I would look for rotors from a well-respected aftermarket part company that knows where the iron comes from. Just my $0.02, FWIW.