The Denix Mauser has brown plastic grips. They're a bit more accurate than the ones you have as they have the 32 line markings. No idea how they compare to the airsoft grip frame, but I do have a bag full of spare Denix grips and an airsoft mauser.
You can replace the Denix grips with wood grips. You have to cut out the center section of the grip frame and remove a considerable amount of the enlarged Denix outer grip frame to fit the wood grips. Because of the curvarture, I usually have to do much of it by hand with rasps and files. I've seen a lot of people skip that step, but its really noticeable if you don't do it. You also have to enlarge the stepped area on the wood grips. When I fit them, I usually do it with a bit of plumber's epoxy between them so they don't drift any. Wakal has directions posted on his site.