I always buy mine directly from S&W.
Inexpensive, too.
Part # 263310000 $3.26 (plus shipping & any taxes).
Might want to order at least a couple of them, plus some mag springs (and maybe followers, if they're worn in a couple of spots), if only to take full advantage of shipping costs.
Call their customer service and ask ...
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Retired LE - firearms instructor & armorer
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