Many countries have well developed camping routes, with trails, refuges and whatnot. If your local library doesn't have specific info on camping in Europe (be careful googling it, most of the answers you'll get will refer to organized campsites with trailers, cabins and whatnot - I don't think that's what you're looking for), then contact the tourism info offices of the countries you plan to visit, asking specifically for information about wilderness camping. They will have plenty of information, I'm sure. I'd get on this pretty quick, to allow time for mailing.
For on line info on German national parks, check out www.germany-tourism.de
Any travel guide will list contact info for camping/national park info in the country information section. Check the books out of the library, no need to buy unless you want to bring them along.
If you live in or near a major city, check and see if there are any consulates, as these sometimes have tourist information as well. If you don't live close enough to visit, you could still contact them and see what they suggest. Some are more helpful than others - I got tons of info from the Korean consulate in Vancouver, less from the Lithuanian Embassy in DC. Oh, and one other pointer - I wrote for information from the tourist info in Germany, and they sent me a bill for three euros for postage.