I use the same oil, here are my sources:
1. First time; Millers Nanodrive 5W30, imported myself from UK, purchased on eBay. Charley Auto in Ngara sell the same, but its not exactly cheap
2. Second time; Castrol Edge FST Professional 5W30, bought from "a guy" :-). Kobil petrol stations do sell Castrol Edge FST Titanium but its 5W40.
3. Third time; XADO Nova Drive 5W30. Currently on this one
4. Fourth time... Maybe I will try out the new Shell ECT oils, the ones they were advertising all over the place recently, apparently made from natural gas. It does come in 5W30