If I understand correctly, you had the BNE-LAX space reserved, but canceled it several times in order to accomidate changes to your domestic Australian travel plans.

If so, you made a huge mistake and learned a costly lesson.

Once you have the international space reserved, never ever cancel it and hope to rebook. Simply call AA and have them switch the domestic flights for you. They can do this without losing the international space.

If for some reason you could not get in touch with AA, you shoudl ticket what you had and then change it when you can call AA. Yes, it will cost you some money, but you won't lose the space.

I would say the odds of that space opening up again are slim to none. You are, unfortunately, likely going to have to find another option.