I am not aware of any other remote that would control the Polycom codecs that have the VCR controls also.
The movement sensor is also unique to the HDX and RealPresence Group Series remotes, though they operate differently. After comments about the sensitivity of the HDX remote the RP Group remote requires an up and down movement not just movement to wake the system up.
Using a 'programable' remote I would imagine you could duplicate the IR codes to the functions of the Polycom remote. There is a section in the HDX Integraotr's Reference that gives you the IR codes.