Does anyone make a 10 round magazine that will fit a 3913?

The one I have is the Lady Smith, but I assume it's the same as any other 3913

S&W factory magazines are recommended over aftermarket magazines for the 3913, and they make a 9-round 3906/909 magazine that works wonderfully. I don't know if any aftermarket makers do a 10-round mag or not, but I wouldn't trust it to be as reliable as a factory mag.

No. As TercGen points out the 3906/909 magazines will fit and function. They will stick out of the bottom a bit.

There are collars made that go around the bottom of the magazine that will fill void created.

There were recently and may still be some for sale on Ebay.

Note that I am not the seller, don't know the seller, and have no pecuniary interest in the listing.

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Can open, worms everywhere.

You can take the road I did and get 9+1 in a 3913:
Pachmayr Mag sleeves for Kahr MK9 on 3913
Working very well these last 300 rounds or so.