Where do I find this file?

[LogWhat1]

I want to modify an older version of RoR. I want to replace the mesh cpp with the new one. But where do I find these files? I can't find em anywhere.

21:51:42: OGRE EXCEPTION(7:InternalErrorException): Cannot find serializer implementation for mesh version [MeshSerializer_v1.100] in MeshSerializer::importMesh at C:\data\codehg\dependencies\src\Ogre\ogre_src_v1-8-1\OgreMain\src\OgreMeshSerializer.cpp (line 182)