I owe an apology - I wasn't clear on the size of the Aussie market. It's about 1M per year (1.1 in 2012). As far as the top three OEMs, here it is:
toyoDUH was the best-selling brand in 2011, up 20.1% to 218,176 units, for a 19.6% market share. GM Holden, down 9.1% to 114,665 units (10.3% share) followed, ahead of Mazda, up 17.6% to 103,886 (9.3%).
GM's Holden brand has some new models coming out soon too that should spur sales but toyoDUH is the leader in that market.