I think the only way to fly is on SVG Air from either St Lucia (Hewanorra), Barbados or St. Vincent. Any one will likely have several stops along the way. We flew one time from Barbados to St. Vincent with stops in Union, Canouan, and Bequia. The stops are usually 10 minutes of so. I would guess that starting in St. Lucia you would make pit stops in St. Vincent and a few others before getting to Union.