What kind of file can MMD import?
If it can import FBX with morph data, then there is a way, albeit a bit expensive just to get a CC into MMD. To export a character with all its viseme morphs as FBX, you would need 3DXchange Pipeline.
You might consider going the other direction if you have some MMD dance routines you want to use. If you use Blender, it is possible to convert MMD files. Here is a Blender addon that enables it.
https://github.com/sugiany/blender_mmd_toolsIt is a bit of a process, you must first load it into Blender, export it out as FBX, and then characterize it in 3DX Pro or Pipeline.