Ok^^
The German Singles you should get in every normal Record store, but I think that you must order it there, because they donīt have them in stock i think (except the newest "appears") *but the most stores canīt order M anymore, so this single is very hard to get*
J-pop Cds are very hard to get in Germany. I donīt know where in Germany you will go, but in Berlin and Munich there is a store called NeoTokyo that sells J-pop/J-Rock CDs. You can find Infos
Here! *You can buy German Gackt Realases there^^*
And in Düsseldorf and Franfurt/Main there are also Japanese Bookstores that have some CDs, but I donīt know the addresses^^;