Are you looking for a live oyster? This would be difficult to do as they are very delicate creatures and do not easily handle transportation. They are collected as spat at farms and grown into maturity on location.
You are not looking for that "pearl in an oyster" thing, are you? I do not know of a company that does this with Tahitian pearls as it would be simply too expensive. And the process with which they do it with kills the oyster anyway - they place a whole pearl in the oyster, place the oyster into a formaldehyde solution so it closes (and dies) then sell them in little shops. Big surprise that every oyster has a pearl - eh? What irks me is that every sales person has been trained to lie to the unsuspecting tourist.