Browsing through the Forum.hr site's topics covering history I came across a thread where one of the forum members started to share his collection of 1:75,000 old military maps covering Croatia from the time of Austria-Hungary (early 20th century). If that's not enough, post #221 has a link to a huge collection of topo maps of former Yugoslav republics. The scale for the maps vary. For Croatia the site has 1:25,000 ones (grid), just like for Slovenia (grid), Serbia is covered by both 1:50,000 and 1:100,000. There is also a section for Crna Gora (Montenegro). These maps were made in the 1970s.