What a hilarious lot you are.
I could make my own but time is short and ready made handles are inexpensive, probably cheaper than the material would cost.
I expect to have to do some fitting but as far as I know you can't "shave up" a handle that is too small.
If I "search correctly" I find many suppliers but very few that specify by eye size as well as length. Length isn't an adequate way to specify a handle. Richard Carter for example only quote length and apparently don't sell to consumers anyway.
Handles are not cylindrical, a 16" hammer handle with 2" sawn off isn't a 14" hammer handle, it is a 16" handle with the end sawn off.
The most important dimensions are of the eye but on consideration I think that I would prefer a handle 12" – 14" long.
W.