Heaps of availability using google flights multicity option. It starts out saying $3000 AUD but then drops down to just over $2000 AUD (1400 USD) as you choose TK flights. The US city options are IAH/MIA/ORD/JFK/IAD/ATL; I went with ORD, somewhere I've never been before
I've got with a week in IST and 4 days in ORD.
The best part is you can pay up to 3 days later it appears - I've elected to take this option so I can check I'm able to take the leave at work tomorrow! Hopefully doesn't reprice - though it says that the price is guaranteed with a USA port.
Thanks OP and all contributors.