"OSL-Seoul-Perth-SYD-BNE-SFO-New Orleans-BOS-LHR; later LHR-OSL" [ OSL-ICN-PER-SYD-BNE-SFO-MSY-BOS-LHR;LHR-OSL ]
Some of those do not exist as non stop flights. But you have segments to spare.
Link -- > A map from the Great Circle Mapper - Great Circle Mapper

Example- QF only operates BNE-LAX. And SYD BNE can be cheap to buy with cash.

Wikipedia airport entry generally lists airline & routes, but not always up to date or list future routes/routes to be deleted
https://en.wikipedia.org/wiki/Incheo...tional_Airport

And https://www.flightconnections.com/

And https://flights.oneworld.com/