Drop Shipping different sizes and with google sheets!

Hey Guys! Need some help. My home base is the US but I’m trying to set up a drop ship option in Australia for national orders but I can’t wrap my brain around how to do it!

I print from home but only up to 16x20" and the Australian drop shipping company can go super large so my sizes are naturally different(plus great plus options). – Is there a way to create a separate page that is only accessible to australians with specific sizes? How do I do it? Or does it need to be cohesive across the board?

Also, they use a google sheets system for orders. Is there a simple guide you may know of that can help unwrap my brain from this confusion?

Any help would be greatly appreciated! Thanks heaps!