SciBit now also maintains our own libmysql.dll which supports both old and new authentication and is only 157KB in size. So if you absolutely have to use a dll (instead of the Direct driver), then you can download it from MyComponents
Unlike MySQL's newest clientlibraries, which are 1-2MB in size and is usually not versioned, does the SciBit library contain full version info, is small and works 100% with the MyComponents. NOTE: It only implements the API needed by the MyComponents, which is minimilistic, so don't go replace all your other apps' libmysql.dll with it!
It is also free, and contains 0% MySQL source code (it is written 100% in native Delphi) and therefore does not carry any licensing issues for your commercial applications.