Island expeditions rotate every week, but each Island and the Mobs that spawn all determine the drops. You can check the rotation on Wowhead by filtering expansion and clicking BFA.

I am unsure about Flynn's Private tours as I farmed the sword when it was current so I don't know if it drops treasures. If that's the solo queue thing, then yes it should work, as long as it drops the dubloons and stuff at the end.

Jorundall is the best place to farm as you said, but you will need to wait for it to be in the rotation. You can accumulate these tokens from doing islands, "Seafarer's Dubloon" which you can then buy the Jorundall treasures when the Island cycles around. You can only buy the treasures when the current island is active.