Its not something that is generally sold on its own. If you really think it is that, just put a thin bead of silicon where it was, and let it go off before testing it.
Although, I have never needed to fit one to improve suction. On some machines they may be missing but it makes only a very small - if noticeable - difference.
Seldom will a clutched machine lift carpet anyway (assuming it is clutched).
Have you checked the bottom hose?