I got my true south information from the house allotment plans that give the boundary true bearings. From the pegs, some string (measured length) and trig tables I was able to plot a true north south line through the base of the telescope mount. Maths we learnt in first year at high school. Sorry for you poor chaps who go to schools that think maths is a waste of time.
You can also do this from google earth with a bit of maths and identified points.
Barry