Hello, Pálma! I've got access to some books called "Aula Internacional", they go from beginner to B1. Now, I'm not saying that there aren't books that focus on advanced learning level C, but I'm having a bit of trouble finding them.
Reading upon the DELE C1 - C2 exams, it seems to me that you need to be confident and fluent in several topics, such as:
- Health, healthcare, medicine
- Economy, finance
- Education and related topics
- Leisure, hobbies, what you and other do with your free time
- Working, jobs, professions
- Social media, social networks
- Science and technology
So, in case you do find a book that focuses on the advanced levels (C1, C2), still I would suggest that you try to find out the current topics that they tell you you should study for the exam, and I would start by preparing for them, reading about the topics in your own native language. I would study these topics to know a lot about them in my own language, and then, what you would do is you'd create flashcards or your own "mini-dictionary" with the words you need to be able to translate whatever your opinions or written documents say to Spanish. All the vocabulary, and expressions, you can find online, or in forums or websites like these.
I hope you find this suggestion useful, and let me know if I can be of further assistance, my native language is Spanish (Latin America). Practice makes perfect!