Chillout is okay, but they are not completely into trance.
Gosapiens is just one organization, there are others like STS or Xperiment.
Vistit these sites and forums and you`ll have the most up to date info on all parties (big or small) in Serbia. Most of them have an international section so there won`t be any language problems.
www.psyserbia.com
www.gosapiens.com
www.xperiment.co.yu
www.stsmusic.org
Hope I helped. Cheerz