Synchronizing Delphi threads: missing primitive?

I just need to use the documented feature TSynchroObject (in the online
help it is said to be placed in "unit syncobjs").
I cannot seem to find this unit anywhere, neither as a DCU-file, nor in the
source directory.
I have the "Delphi 3 professional" CD-edition.

Does anyone know where it is?
Did Borland simply forget to include it?