As you probably know, Christl is primarily a first name, a short version of Christine and similar names. As a last name, it is not that frequent.
When you go to the Austrian phone directory (white pages) at www.etb.at
, and restrict the search to Oberösterreich, you will see that there is a listed number of Franz Christl in Braunau am Inn, town of Haselbach.
However, Braunau is quite far away from Kollerschlag, and Gmunden is nowhere near either.