Americans citizens, Europeans, British, Australians and Canadians DO NOT require a VISA to visit St Vincent and the Grenadines (Union Island). Your passport should be valid for a minimum period of 6 months. Note: Nationals not referred above are advised to research on line for visa requirements.
A return or onward ticket is required by all visitors, as well as proof of accommodation.
The easiest and only direct way to fly to the grenadines (St Vincent) is to fly to Barbados or St Lucia which has daily connections to St Vincent and the Grenadines.
Fly to Barbados Airport (BGI) first and get a connexion. We will be able to pick up you on any grenadines island if this can make it easier for you like union island.
You can use search engines like Expedia to find the flights that will suit you best.
London or other major cities have daily connections to Barbados (BGI) and Ste Lucia (UVF).
Once arrived on Barbados or on St Lucia you will need to take a final very short connecting flight to St Vincent or Union Island with Mustique airways or SVG air . (same flight share by both companies).
You can use search engines like Skyscanner to find the flights that will suit you best