I don't know of any Theravada groups in Cairns (sorry) but you could contact http://www.yuloling.com/
As you will see, it is Vajrayana, but Ven Rinchen is friendly, sensible and helpful. She will tell you of other groups in Cairns if there are any.
If there aren't, you might consider going along to Yulo Ling just to have a group to share with and encourage your practice. It might not be exactly what you want, but it might be better than nothing.
I guess the other alternative group choice would be a yoga or tai chi group, and I'm sure you will find several of those.