Did not find any online.
If you just want to get rid of Force March completely, you may delete the file force_march.txt located in \\ImperatorRome\game\common\unit_abilities\
Making it into a mod yourself would be recommended, that way game updates will not bring the file back in the future.
If you do make it into a mod (to disable the ability), you need to overwrite the file by placing a copy of it inside the same folder structure in your mod but deleting all the text within it.
EDIT: Made it into a small mod.
You can extract the contents of the .ZIP file into \\Documents\Paradox Interactive\Imperator\mod\ so that the folder's contents look like
[_] FOLDER : RemoveForceMarch
[_] FILE : RemoveForceMarch.mod