I was able to find this:
Yamada-kun to 7-nin no Majo OST (Music Collection) - HikarinoAkari OST (http://hikarinoakariost.info/yamada-kun-to-7-nin-no-majo-ost-music-collection/)

But i dint found the full OST, im looking for a song instrumental with a nice guitar arrangements.

I already created a topic about that here a few weeks ago, I am still hoping for a positive answer^^

Finaly found the it here https://mega.nz/#!30BBzb7D!jE7NF-LwqK_8xEN9cr2VDnVrHGEGeRyvqtVpa1-yHo4