Where else can I post adverts to do with Cambridge?
cam.* isn't your only option. Other places you could try are:
Cambridge University runs a set of newsgroups, including ones for things for sale, things to give away, computers for sale, and things wanted. See the list of Announcement and Advertisement Newsgroups
for full details. Only those within the university can post to these directly, however other people can post to them by crossposting to another (preferably relevant) newsgroup at the same time.