S&W no longer makes the Combat grips so finding a "new" pair might be difficult. Sometimes they surface new in the package.
You can keep an eye peeled here for some in the WTS section or check the major auction sites.
I have had good luck getting a couple pair in real good shape that way.
Prices can range from $200 to $300 give or take.
Another option is to check out what is offered by Culina Grips.
They make a real close second to the originals only the wood selections are vast and many. The cost isn't much more than finding a pair of the originals.