The particular GA grips I have on the steel frame Model 39, where hand selected by a former (now retired) Smith&Wesson employee because of their color and grain (the picture does not do them justice). I was able to buy them from him a few years ago, to put them on this steel frame because the contrast of the wood against the bright blue steel finish is great.
The GA grips as well as Rosewood grips were available as a option from the parts department, similar to revolver grips. Most Model 39's were generally shipped with Walnut checkered grips. I have seen/noticed that some Model 39's had been shipped with other than Walnut grips especially engraved models, and special order guns.
There are alot of Model 39 grips for sale on many different websites, so you probably could find a pair of similar to these for sale. I was lucky that the gentleman who sold these to me had a good eye, and was able to pull these for himself through employee sales.