Do you want original S&W wooden grips to keep the weapon original, or just replacement grips (by S&W or other companies) to replace the old ones when shooting the weapon?
I've seen lots of auctions for original S&W grips; check the gun auction sites for these.
If there are any gun shows near you, then I'd make a few passes through the show and ask folks who had grips on their tables if they had anything to fit your weapon.
CDNN has a few sets of wood grips for Square Butt K-frame revolvers:
Smith & Wesson K&L Square Butt Coco Bolo Grips w/Medallion New
Smith & Wesson K & L Frame Square Butt Deluxe Walnut Custom Grip New
Hogue makes very nice fingergroove wooden grips, in plain or checkered patterns, and various wood types. Their prices are high, but the grips are great.
You can find Hogue grips at MidwayUSA.com (although their search function sucks; be prepared to do a lot of browsing).
Finally, the S&W website has some selections in their online store:
Product: K/L Square Dymondwood Checkered Service
Product: K Square Rosewood Combat Grips
Product: K & L Square Butt Traditional Checkered Target Grip With The S&W Medallions
Good luck finding what you need!