Hogue hardwood grips for the PPK will fit the Fort Smith model. The inside of each grip half has a locating pad that will need to be lightly (no power tools) sanded in the locations shown below:
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It's easily done with a file. Just file a little then check the fit. You don't have to take off much. If you don't do anything stupid like trying to use a dremel, when you're done, they'll look like this:
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That's checkered rosewood on the black one and checkered cocobolo on the stainless.
One note. If you look at the stainless one, you can see that the bottom of the grip is just the tiniest smidge below the frame. I only use the flat base mags, so no problemo, but if you use the finger rest mags, the rest might interfere with seating the mag and you have to give it a good whack to seat it. Or you can remove the finger rest, lay it top side down on a piece of sandpaper and rub it back and forth until you remove enough. No more than 1/16" I think.
If you want something fancier, Hudson River Valley Customs (hrvcustoms.com) gets plain wood grips from Hogue, Altamont and another company I've never heard of and does custom work on them. I have a Hogue grip from them, and it's really nice, but I prefer the plain checkered grips.
Obviously, since I don't know anything about that third company HRV uses, I can't judge them, but I'd be careful about Altamont grips as they have QC and customer support issues. My wife and I have had multiple problems with them and won't buy them again.