Talk to Dusty on the last sand isle, you can find him inside his house. To get off Dust isle, you'll need to find Fitzgerald, who is always located near the cacti.
you can find pixie dust on the ground on Cloud Isle (you need 75% qp and 3 giant coconuts to get there). you can also check general stores or ask other players to see if they have any.
There are two ways to get to Unknown Isles on HI. First, you can rent a pegasus Cloud Isle, once you have the 75% QP award. It costs $1,000,000, and you have two real hours to ride around, over water...