Sports bars? Any bar owned by an Australian with a TV will have both grand finals on - that curtain-raiser on Saturday and the proper one on Sunday.
This place definitely has it on live: http://www.sportsbarbangkok.com/
And here: http://www.downunderbarbangkok.com/
And here: http://auswathai.activeboard.com/forum.spark?aBID=127609&p=3&topicID=28422996
And here: http://www.theofficebkk.com/
Maybe also Hanrahans or Strikers on Soi Nana - Gullivers on Soi 5 Sukh - the Sports Corner on Soi 20 ...