Its not difficult to add the extra 'fin', any machine shop can do it. They can easily measure the existing 'fin', make a piece which has 2 fins, make a cut in the middle of the grip area and attach the new section by screwing everything together. A bit of JB weld would make sure nothing will come apart. And if the joints are at the bottom of the 'valley' they'd be invisible, especially after painting.
An extra section with two fins need to be made becasue when you make a cut, part of one fin will be damaged, its just how a lathe machine works. So the shop will need to cut away an entire fin, and put back two.
Problem is, not many machine shop want to do small jobs like this, unless you know them real well...
I recently tried to get a grip section with uneven fins made as a special request for a member here but even my regular machine shop won't take the order.