Use Google Flights to search for dates. Here is a sample trip from SFO-SYD for $581.
Flights will be purchased from Delta. Check Where to Credit to find the best place to credit your miles. Chances are, it’s not Delta.
Dates: Valid until November 30, 2016.
Requirements: Purchase at least 14 days in advance, 10 day minimum stay.
Stopovers: One free. Options are Sydney, Melbourne, Brisbane, or Los Angeles.