This is my 3D-printer, and I am looking for it's
.stl parts to print. Also I don't know which kind of Prusa is it?
I would try Googling your specific make of the i3. For example if you have a Geeetech Prusa i3. I would type in Google "Geeetech prusa i3 stl parts" and I'm sure you should fine plenty of things.
If that is unsuccessfull. I guess try this one. It looks similar but it lacks that hole on the bottom middle to the right of the motor holes. So if its not important, I would look at this. https://www.thingiverse.com/thing:1103976. Might be a good idea to replace the entire X axis system with a new printed one to make sure it all fits and works.
@Tom van der Zanden is correct that without your specific version it is impossible to find the same part since small variations such as the distance between the two X axis smooth rods may differ between parts. While it is almost standard for the i3 design, you will find minor changes between variations.
I would also try scrolling through here. https://www.thingiverse.com/groups/prusa-i3/things