Lowes?
Seriously, I'm not sure exactly what you want, but try an RV dealership with a parts department or a Camping World store. RVs have venetian blinds of all types on some strange shaped windows.
I would have to go with this one in America. Sure the aussies have them down there but unless you want to pay extreme cash for shipping or planing a vacation.......
Sometimes the local lowes store may surprise you.
