Well, the best thing is to provide us with a picture of this watch
April 10, 12 19:59
both the front and the back so that we have a better idea of the watch you have. As for auction websites, I believe you are best off looking at Antiquorum, Sotheby's, Christies, or Bonhams as the authenticity of many items on ebay is questionable. The quickest way to do this is to do a search on google along these lines: "Antiquorum + Vacheron Constantin + Overseas" and you will have lots come up in the search result. Same approach may be used for the other auction houses (i.e. for Christies, you type "Christies + Vacheron Constantin + Overseas").
Best,
Walid