Attila
I have heard of the pear, but have never seen one, or know how to obtain them. I have seen Malus sylvestris seed for sale. Both sound like excellent candidates, especially if they could be collected from the field. I have a small Asian pear that I got from Jim Gremel. It was supposed to be Malus toringoides, but turned out to have pears! We think it is species Pyrus calleryana or P. ussuriensis, or another small Asian Pear. This is one of my favorite trees and will be a stunner in a few years. It was field grown at Jim's place for about ten years and has a wonderful moving trunk. It should finish at about 10 inches tall. Trunk is done, just have to work on the branching. There are many species of wild Prunus, Malus, and other fruiting trees in the US that would make great bonsai. I am sure the same is true in Europe.
Brent