Sencha is probably your quinessential Japanese tea. You should be able to findit online from many source and in many forms - loose leaf, pearl and powdered, even in tea bags.
Its is rather astringent compared to the sort of black or oolong teas usually served in England and probably in Germany )is been too many years since I was there to recall for certain).
One of my favorite sources for tea if I have to get it shipped is Ten Ren. They are good about their quality and variety and their staff is very knowlegable if you have questions.
Ten Ren Tea