An acetone soak with multiple deionized water rinses is possibly your best bet with the silver medals/coins.
Though the pictures posted of the medals being handled is concerning I have trouble giving much credence to a forum owner who calls the Chinese sponsors and dealers "Ball Sweat Monkeys".
Those are the rantings of a deranged mind IMO.
Alas you make the same mistake many others continue to make the world over; trying to explain away gross misconduct and bad deeds on the basis of mental disease. This is nothing against you personally but that's how it is. You probably can't imaging how a sane person can say such things. But they do!
The "insanity plea" has never withstood critical legal and medical evaluation in the law courts except in very few instances. I have been dismayed at how well meaning people have been denigrated as they conduct their normal lives and social interaction. It is revolting to say the least but not unique; there is at least a recent history of increasingly foul language mixed into the usual diatribe. I have tried to keep away from it all but continued politically correct silence by all witnesses has to be regarded at some stage as acquiescence and complicity with what is been done.
It is paradoxical that the same individuals who have innovated a highly regarded medal series are now being dragged in the mud with onlookers just watching. This medal series has led to increased MCC collection offerings. Many mouths are being fed from the venture from design to production and marketing. It has provided material to keep segments of online forums ticking along nicely. The very people who are "feeding you" are being insulted. They are not just alone in this maltreatment; all associates, family and (dare I say) country folks, by association and proximity, have to bear the insults too.
There is a group of individuals in this world who think somehow that it is their God given right to exploit others and put them down at the same time! Unfortunately there is also a larger group that just standby and watch!