As Brett mentioned, if you know some one with a good hand at the TIG welder, they can be welded up and you can retap to original. Strip the engine down, and I usually grind away a section so I know I am reaching all the way to the bottom of the hole. You can heat the case for as long as it takes to boil out the oil in it, and there will be oil, but I usually just preheat the case, and with a patient foot on the pedal, heat the area with the TIG torch and let the hi frequency help scrub the area. You may have to stop from time to time to re grind the garbage away, but when the oil is gone you will just suddenly see a nice, clean aluminum puddle, then just add until you get what you need. You can't rush this process, just do what needs to be done. Practice on an old case if need be.
In machine repair at work, some times welding wasn't an option either. And if I didn't have a Keen-cert or heli-coil the correct size, I would make one by picking the appropriate bolt or screw size, and then drill the center out for the tap size I needed. Get a length of bolt all drilled and tapped, and then dril and tap the part for the bolt outside diameter threads. Cut off the length you need, grind a slot on one end for a screw driver to catch it, then apply loc-tite to the threads and install. I have had this work very well on many occasions, you just need the appropriate machinery and tools.
Good luck with it,
Dan McEntee