You should be able to get a few recoil springs from S&W. Call customer service. As a matter of fact, if you only want one and speak kindly about S&W, they may put one in an envelope as a courtesy.
Here's an excerpt from the current parts list for 4516:
59 108660000 $1.45 X RECOIL SPRING - OUTSIDE
59 108670000 $1.45 X RECOIL SPRING - INSIDE
59 201330000 $1.45 -1 RECOIL SPRING
You want the part no. 201330000