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I guess you mean "ImportV3" plugin of "はちゅねのないしょ" (Hachune no naisyo).
You can download it from

First install the current version of はちゅねのないしょ
(Never use the older versions!) as follows:
Download naisyo***.zip (*** = version number) and unzip it.
Copy "Plug-in" folder and msimg32.dll into the folder where VOCALOID2.exe resides
(e.g. C:\Program Files (x86)\VOCALOID2).

Then install the ImportV3 plugin as follows:
Download ImportV3_***.zip (*** = version number) and unzip it.
Copy ImportV3.hmp and ImportV3.ini into the Plug-in folder
(e.g. C:\Program Files (x86)\VOCALOID2\Plug-in).

That's all. Run vocaloid2 editor and now you can import vsqx files into the editor.