BB270, try Brownell's for extra magazines. They are not Winchester made, they are after market made by Twine Pine Inc. I don't know personally of their quality, as I have not used them, but Brownell has them. http://www.brownells.com The part number is 895-100-100 and cost is about $48. Original Winchester magazines are listed at Bob's Gun Parts and Gun Parts Corp., but they are a bit pricier at about $50. http://www.gun-parts.com or http://www.e-gunparts.com

Like everyone else said keep the extractor clean and the chamber lightly oiled, and you shouldn't have any problems with it. I run a lightly oiled patch in the chamber on mine every so often and never had a failure to extract. I have had a failure to feed a few times, but it appeared to be operators headspace and timing error, not the gun's.