The M1 Garand extractor and plunger/spring are identical to the M14. You may be able to find one at Marstar or another Garand parts source.
When installing a new extractor make sure that the vertical post doesn't extend below flush with the bottom of the bolt. If it does there is a good possibility that it will be dislodged by the bolt passing over a round in the magazine. The solution for this is to grind down the bottom of the extractor post so that it is slightly below flush, or at least flush, with the bottom of the bolt.