On Margot McKinney's website, she says her Australian South Sea pearls come from Ellies Pearling. There's a documentary on her site, "Beneath the Surface." "The film titled Beneath the Surface (2019) is the story of Aji Ellies’ pearl farm now based in Arnhem Land. Traditional Owner Terry Yumbulul stands on the beach, tracing the protrusion of a blister pearl on a Pinctada maxima shell, as he relates the way Aboriginal people grafted pearls onto wild shell generations ago. They pioneered a technique for culturing pearls, adapted by Ellies today."
ETA: The video is 17 minutes. It's pretty good.
There are several choices of these enormous pearl necklaces on her site, price upon request.