Not in the RS guidebook...Croatian for Mr and Mrs.
When addressing a stranger, would you say...gospoden/gospoda...before your question to them?
We always try to learn the basic words & phrases before visiting.
What is commonly used?
I would just say Dobor dan (good day) or dobor veche (good evening). I have never heard anyone say "gospoden". But if you say Dobor veche they will say "You are really learning our Croatian language". Also "hvala" (thanks) or "hvala hvala" is helpful
I agree with Paul. Dobar Dan is perfect. Means hi and a good day. At evening you can say Dobra Vecer. In addition to this what I can add as a host and traveler: always approach with happy news. Hi I am Ray, I really love Croatia.. be passionate and adapt to situations. Most of the travelers come at reception 'we wait taxi long, it is hot, it is far, where is my room'.. take your time and enjoy what is there. no need to be active in way i want to change it on my way. This story is maybe not for Croatia but I have seen it many times. Every new step is new life scenario and you are the actor :)
Have a nice lovely and safe trip.