The ones offered by Numrich (e.gunparts.com) are the closest copy to the later convex style smooth 1917 grips I have found, and they are pretty cheap at $36 a pair. I bought 10 pair and I've been working at checkering some of them in my spare time to resemble 1920s and 1930s styles. I'm hoping to eventually make myself a good copy of all the pre-war styles using them as a basis. They are nice walnut and fit pre-war frames very well. The ones I've seen on the auction sites for $60-65 don't fit as well and are finished all wrong.
Originals do turn up on Ebay and Gunbroker from time to time. If you know what to look for, I've seen (and bought) a few sets that were mistakenly described as WW2 Victory model grips. It takes a lot of practice to be able to recognize the difference of around 1/16" in a poor ebay picture.