Where are open clusters found in our galaxy?
Pretty much all over.
An open cluster is a group of stars all formed in the same nebula some time ago. If you look, currently there are hundreds of nebulae in the Milky Way Galaxy, and previously there were many more.
While there are nebulae all over our galaxy, a large number of them can be found about 15,000 ly between the center of the galaxy and our own position in it. This trend in distance from the center continues all around the galaxy as far as we can tell.
Therefore, many of the open clusters can be found in such areas, although in lesser numbers they are found throughout the galaxy.
If you would like to see some of the ones visible from earth, consider looking at some of the Messier Catalog, or a sky atlas, my particular favorite is Uranometria 2000.0.