There are also "backroom" sales, where these sorts of items can be sold in countries who have been embargoed. You trade this type of painting for a ridiculous amount of an embargoed country's goods or something and then you can smuggle this into Russia or China to trade for a non embargoed currency with an oligarch, since oil prices have plummeted. They, in turn, can hold on to it for a few generations, and sell it in grey markets for a good profit and some time.