At the top of the download page it states:
NOTE:
For IPS MC 2.1 please proceed to the VMS blind rev page and download the appropriate VMS 2.3 bundle installer (Windows or Solaris) and then apply Service Pack 1 from this page.
The "VMS blind rev" page reference is a link to the correct place on CCO. So follow the link to download the VMS 2.3 components (includes IDSMC 2.1 files inside it).