I was wondering where do all the big coin websites get their shipwreck/admiral gardner/Dutch VOC coins from? I would assume there is a wholesale source somewhere. I was looking to buy a large lot but don't know where I could find them at an uninflated price. I would assume they get their Roman coins pretty cheap in bulk and I would be interested in the same thing but buying at retail price is not an option.
Shipwreck sites in Western Australia have all been administered by government agencies such as museums. They control what is taken from shipwrecks. It is through their agency that items such as coins find their way on to the commercial numismatic market, and the proceeds from these sales help to fund the costs incurred on diving on the wrecks.
Basically, the source for the shipwreck coins are the museums. That certainly applies to Dutch coins that are found on shipwrecks that lie off Australian coastlines.
The X CASH and XX CASH from the Admiral Gardner shipwreck located on the Goodwin Sands in U.K. waters are found in large numbers on the international numismatic market. I have a few examples of each denomination. They originated from an entirely different commercial source, after being recovered from this shipwreck. A Google search should provide much more information
Identifiable Roman coins recovered from shipwreck are rare, and almost all are too heavily corroded in a sea water environment to have any real numismatic value. Most ancient coins are recovered from ground burial anyway, not from shipwrecks.
Not much chance for 'johnny come lately' numismatic collectors such as myself, to be able to buy shipwreck coins in bulk directly off shipwreck diving companies.