Can my Australian friend obtain a 6-month METV in Brisbane?

Agree with this - even on a 6 mo METV you only get stamped in for 60days so you still need to extend for another 30 days at Immigration and then do a border bounce to get the next 60 days and then a further extension. Unless they will be staying right on the border and so can just bounce in and and out each time for a new 60 days, without the need to travel to a border or extend at immigration, it will probably end up being more expensive than 2 * single entry visas and 2 * 30 day extensions.

phew

I am not sure about the AU requirements. But if they wish to stay in Thailand for 6 months then I suggest they obtain a 6 month METV. I expect others more familar will reply soon.