In Repairing a Broken Kidney Gearbox I detailed a method for repairing broken kidney gearboxes. This is not the only way to do it, but it is a good way and worked well enough for me. 

The kit being sold here includes one mild steel flange as well as two washers to be sandwiched in front of and behind the broken gearbox flange. Purchase this kit plus some 5-Minute Epoxy or JB-Weld to complete the installation. 

Refer to my blog linked to above for instructions.

Price is per set of one flange and two washers and includes shipping within the continental US.