How can I find the best cobalt alloy powder from China?
Look on the internet. THEN see if the same source claims to have FOOF for sale in greater than microgram quantities. At least one Chinese source claims to be able to sell kilograms of the stuff. FOOF, Difluorine dioxide. Yes it has been made, yes at least some makers have survived.
Personally visit the day care centers where it is being mined and processed.