Here are few tips from Mika, where you can buy electronics components. There are many other shops in the world… so you can find your own choice. These are the ones convenient for buying in Berlin, or shipping in Germany.
A lot of Sensors and Arduino related things come from these online shops. They have tutorials, discussions, forums so on, so even it is US based shop, it is worth checking
As above shops are in US, it is not so easy to buy from them directly as shipping is quite expensive, and you have to take care of the tax sometimes. Here are retailers in Germany who sells their products.
https://www.tinkersoup.de/ (this is Berlin based, and you can pick it up directly from them if you need it quick. It is in Friedrichshein. We have also discount coupon, ask Paula for detail )
For electronics components, you can go to these shops in Berlin
(physical shop in Charlottenburg)
http://www.conrad.de/ce/ (They have some components at shop, but often have to order online and pick it there. It is at hermannplatz)
For SMA (Flexinol) I bought it from here: