Hi Ivan,
Just read your intro, and I noticed you are 12, which is somewhat younger then I expected.
With bonsai, there is one thing to keep in mind: IT is a hobby which takes years. So a course which starts only in 6 months would still be a good idea (I Actually registered for a workshop in the UK, taking place in November I think. It sold out in May...)
All in all, if you go through this website and read the tutorials, you should be able to find out a lot already. Also, if you look on the internet for bonsai Kroatia, you will find a few people with websites. Contact them, and ask around a little.
I think I saw Walter Pall as one of the persons with good contacts in Kroatia. He is a VERY good bonsai Artist, and very helpfull. I visited his gardens this summer near Munich (He is german). I am sure he can introduce you to some people, if you pop him an email.