After many phonecalls found a hardware shop that was pleasant in dealing with my questions, and that without weird financial requirements. They'll be sending me an email with various options soon, and then I can order without a hassle. And without extra costs. Hurray for them.
First store I called was pleasant enough with their answers. But then they told me that I had to pay €15 at least for an order of a few euros. And it would be a gamble if it would fit neatly.
Other stores acted weird about the measurements I needed. Apparently knowing your data is not enough in a technical world.
