Boardgames market is quite weak in Slovenia. There is only one shop in Ljubljana that is specalised in boardgames... http://www.laserplus.si/cluknja/ Unfortunately everything on webpage is in Slovene. If you want some concrete info, feel free to ask.
This is a super old thread, but I wanted to add to it as an update for anyone who is visiting the lovely city of Ljubljana!
Crna Luknja is still there, but it should be noted that it is closed on Sundays and is only open 1-7 PM on Mondays...The other days of the week have much better hours. It has a nice selection of new and old games (some out of print in the US!) in several languages.
There is also a toy/game store near the river called Tojeto. It has a nice selection of games as well (and the staff is a bit nicer).
It should be noted that there appears to be a meetup in Ljubljana about twice a week!