The headsets off the Animasa Vocaloid models which come with the MMD download. They are:
Miku Hatsune/Miku Hatsune Ver.2 & Metal/Haku Yowane
Rin Kagamene acts 1&2/Len Kagamene/KAITO
Animasa MEIKO and M2's Neru Akita do not have headsets, and Kio Meiko Sakine is not included as she is not an Animasa model.
The Animasa rules apply. As far as I know the only thing that is not allowed is commercial use - apart from that you can edit, use and redistribute all you like!
Each headset comes with both a .pmd file and a .x file. The .pmd files have mother, centre, head, neck and bones so they can be attached to models without having to manually rig them.
Please note that these models do have a few glitches. I have endeavoured to remove most of them, but please note that:
It is best if you load .pmd files for the Rin Kagamene, Miku Hatsune and Miku Hatsune Ver. 2 headsets BEFORE the others, as otherwise MMD may freeze. I don't know how much this applies to other models but as you can see they work perfectly well if you take this precaution.
The .pmd file of the Len Kagamene headset has a small rigging glitch whereby it does not move with the mother and centre bones. This will likely be fixed when it is attached to a model. You can also rig it using Pmd Editor if you wish to fix this glitch (I was lazy and wanted to get these posted LOL).
If you have any questions or problems, feel free to comment and ask me. If I can't help you leave a comment at one of the MMD-related groups this download is featured in, and someone will probably be able to help.