The pink topaz and diamond brooch (now mounted as the centre of the choker) and the matching earrings were bought at auction from Sotheby's on 13th June, 2000. I do not know, though, if the buyer, at the time, was the Prince of Wales or Camilla herself, or if they did acquire the jewels later. The topaz and pearl choker was first worn by the Duchess of Cornwall on 17th May, 2008 in Windsor, at the wedding of Peter Phillips and Autumn Kelly.
I do not know the origin of the other chokers. The ones with the aquamarine clasp, the amethyst clasp and the garnet clasp (though I am not totally sure about the latter) were worn by Camilla prior to her wedding to the Prince of Wales in 2005.