You can also try an eBay search to see a number of choices, including original Smith & Wesson guide rods.
Should you choose a used S&W guide rod, it's strongly suggested you likewise acquire a new Guide Rod Recoil Spring so that you are assured of the spring's proper loading for your gun. I've shopped
Wolff for years (in fact, just yesterday ordered nearly $300 worth of springs from them).
With respect to a new rod and spring: The "spring" itself is gonna hand you a learning curve. Take the ride. That spring is an important part of your handgun. Indeed, one tends to believe it wouldn't be there if it wasn't necessary, huh?
Good luck.