I have located a source for original and reproduction parts for "original" 1866 and "original" 1873s. A gentleman by the name of Albert D Buckingham, "The Winchester Man" ion Trenton Tennessee, has parts. Lots of parts. His parts are NOT for Uberti or other reproductions. They (the parts) are for ORIGINAL Winchester guns. I was referred to him for some parts to rebuild a '92.
His catalogue lists link sets (they should be replaced as a pair) for the ORIGINAL 1866. I didn't see an extractor, but you might want to give him a call and ask.
Albert also told me he has about 600+ guns for sale. If your looking for something Winchester, between the 1866 and the 1906, including Mod 67s and 37s, you might want to give him a call @ 731-559-4169. I'd like to take the time to go visit and just browse thru 600+ rifles