For Slovenia this might be of use https://camperstop.si/en/home/
Croatia is really touchy and strict when it comes to any sort of over night stays (at least during the main season and in the usual tourist areas) You do not want to sleep outside campsites unless you're somewhere very remote and leave early. But with so many campsites around I wouldn't bother.
Bosnia, Kosovo, Serbia, Montenegro, Macedonia ...nobody cares much but again, there's plenty of semi(official) options.