Like Phil says, the met reports are a great place to start looking for icing conditions, be it forecast icing or pireps showing icing encountered by others inflight.
Icing is an odd thing though and can be found in a range of conditions. I've flown IMC at -2C and never picked up any ice at all. On another day I flew thru a small localized rain shower at +5C and to my surprise watched the water freeze on contact with the window.
