Hi
EdzuiMM,
Regarding gazetteers, I've looked for one too but not found one online for Austria-Hungary until today.
I had seen a number of references to a fourteen-volume work which covers the Austrian territories:
Gemeindelexikon der im Reichsrate vertretenen Königreiche und Länder [Gazetteer of the crownlands and territories represented in the imperial council]. Vienna: K.K. Statistisches Zentralkommission, 1903-1908
This was published in 14 volumes:
1 - Niederösterreich
2 - Oberösterreich
3 - Salzburg
4 - Steiermark
5 - Kärnten
6 - Krain
7 - Küstenland
8 - Tirol und Vorarlberg
9 - Böhmen
10 - Mähren
11 - Schlesien
12 - Galizien
13 - Bukowina
14 - Dalmatien
This was compiled from the 1900 census.
Brigham Young University has a set and I guess this is what has been digitised and can now be accessed online at familysearch.org.
You can do a simple string search but I believe you have to select one volume at a time.
I've also seen references to an earlier Hungarian gazetteer:
Magyarország Helységonévtára [Gazetteer of Hungary]. Janos Dvorzak, Budapest: Havi Füzetek, 1877.
I don't know whether this includes Croatia-Slavonia or not.
I've not seen any references to a gazetteer for Bosnia-Herzegovina which was occupied in 1878.
My usual starting point is
https://geonames.nga.mil/namesgaz/ which allows you to search for part names without picking a country.
I find it helps to click on the option "Include Historical Records"; however, its degree of completeness seems to vary quite lot between countries.