Sorry for the late reply. I have had no luck finding any municipal courts in the area apart from the indoor ones at St Jakobshalle
http://www.stjakobshalle.ch/en/tennis.asp
I am away in the UK next week and will be bringing my raquet back with me so I'm good for a game anytime in the evenings from the 17th onwards. I will be looking to join a club when I return (any reccommendations gratefully recieved). The courts you mentioned in Gundeli look good (don't understand why they belong to the lawn tennis club when the only courts I saw were clay) but i have been unable to find a website for them