don't know about machine shops, but Stein makes a nice set to repair extractor threads on damaged cranks.. it uses a piloted tap to cut new 24 x 1.5mm threads and comes with some alloy self-extracting type dustcaps to fit the new threads (to be used with a regular 8mm socket crankbolt..) the set we have in the shop also has a heavy duty crank extractor to fit the repaired threads
i have used it a couple times already with full success and, like all Stein tools i've used, it is of da highest quality...
try to find a local shop that has one or get your own here:
http://biketoolsetc.com/
andrei padlowski
ny, ny