If you have enough room (there has to be enough height above the existing CI hub for the flange fitting) above the hub, you'd use either PVC or ABS (whichever is more readily available where you live) to install a new flange. You could use a stub of 4" plastic pipe, which would have an OD of 4.5", or 3" pipe, which would be an OD of 3.5"...I'd probably go with the 4". IF you go 4", you could use a flange that fits inside the pipe, and you can run your repaired subflooring tight up against the pipe. If you go 3", you need your flange to fit around the outside of the pipe, and you'd have to leave a bigger hole in the floor to allow it to slide down and over the pipe to make the connection.
The wall thickness of plastic drainage pipe (well, sch 40 anyway) is nominally 1/4" thick and it's sold by the ID...so a 4" pipe would have an OD of 4.5".
So, if you just tell them you're using sch40 PVC pipe, they'll know what you need, and it should work IF your measurement of the hub opening is correct. Too tight, and you may not get it in, too loose, and it will not seal. It's one of those things where it must be 'just right'. Some liquid soap helps things go together.