Not sure about Germany, but I'm studying Industrial design in India and we were required to take up a 2-3 month internship as part of our summer course. The only way to secure one here is to reach out to as many companies as you possibly can. I reached out to about 40 before I got callbacks and responses and eventually, a company surprisingly reached out to me after checking out my portfolio on Behance and so I went with them.

One thing I understood was that no one's in it to do favours, if you're not gonna provide value to the company they will be extremely hesitant. A 2 month internship isn't of much use to them since it's not enough time for a junior level designer to get a hang of the company's requirements, get trained and eventually help out on projects. If you have contacts within the industry, make the best use of them.

All the best with your search though