They are in 128kbps, but most were converted from flac audio (or 320kbps). So... enjoy!! :)
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2006 ~ N.H.K. ni Youkoso! ED Single, Odoru Akachan Ningen
LINK: https://drive.google.com/drive/folders/0B5UfljZ67vNjUGZDLVFwcEcyVnM
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2006 ~ N.H.K. ni Youkoso! ED2 Single, Madokashii Sekai no ue de
LINK: https://drive.google.com/drive/folders/0B5UfljZ67vNjd3poZmVVMl9HMUk
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2006 ~ N.H.K. ni Youkoso! O.S.T. Dark Side ni Youkoso!
LINK: https://drive.google.com/drive/folders/0B5UfljZ67vNjUWJDRjJETWVHWG8
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2006 ~ N.H.K. ni Youkoso! OP Single, PUZZLE
LINK: https://drive.google.com/drive/folders/0B5UfljZ67vNjSG5XNEsxVi1lSDg
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2006 ~ N.H.K. ni Youkoso! Sound Collection Sunny Side ni Youkoso!
LINK: https://drive.google.com/drive/folders/0B5UfljZ67vNjaHdxdTNiWVp3SHM
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Any problems just contact with me!! (Sorry for my bad english ...)

Thank you for posting. Welcome to NHK's soundtrack seems to just be impossible to find. I downloaded a few of them but was wondering if you still have the .flac files?

Sorry, the old .flac files have been converted to mp3 format.
But I'll search again, if I find, I'll tell you.

Here are the songs in flac audio. I hope you enjoy!!
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N.H.K. ni Youkoso! Music Collection (FLAC)
LINK: https://drive.google.com/drive/folders/0B5UfljZ67vNjZFFTeFM5V0hUaEE