The buying will take place somewhere.

There are only so many coins available...banning the sale of them will only open up the selling elsewhere. There is no way for the government to stop it totally, especially with many Chinese having access to Hong Kong.

Besides, many of the elites/big money people in China have their money outside the country...for the last 5 years they were moving funds out expanding a collapse of the currency. Many of the single family homes sold in the US in the 2013-2015 time period were with Chinese money.