Hi,
Model Engineer magazine has had articles covering oil-firing of locomotives over the years. You don't say what scale/gauge you are modelling in – most of the Model Engineer articles cover 3 1/2" gauge, 'Petrolea', Tich, etc. (from memory). However there may be some info' that would serve as a primer if you search one of the article databases.
Maybe worth browsing Model Engineer Proboards forum too if you are not already a member as there are a large proportion of Antipodes based engineers who may be able to give guidance and suggestions. I seem to recall that the main importer of Welsh steam coal for model engineers, NZ based but sells to Australia too, is an active member. He sells in small quantities, tho' I cannot comment as to the price! Many of the Australian members make reference to using steam coal from club supplies, and using rosebud grates etc., so they may give you some leads/ideas.
Regards,
Phil