I would suggest that you consider purchasing an unlocked iPhone 17 Pro Max directly from Apple.
The iPhone 17 Pro Max is similar to the iPhone 16 Pro Max in many ways – but with a few upgrades. See the detailed comparison here: Compare iPhone Models – iPhone 16 Pro Max vs. iPhone 17 Pro Max .
There's also the little matter of it being available (after preorders are filled) whereas the iPhone 16 Pro Max isn't.
The other thing you could do is to watch the Apple Certified Refurbished Store to see if any iPhone 16 Pro Max models show up there. There's no way of knowing when that would be, or which specific configurations might become available, but it is logical to assume that some will show up there sooner or later.