CableCards (for Tivo DVR) no longer supported?

Via Chat with Cox support I just tried to order a CableCard for a Tivo DVR.  I was told that they are no longer supported and that I can not order one.  I'm skeptical that this is really true.  I always understood that cable companies were required by federal regulation to support customer-owned equipment.  Does anyone know more about this?  Would be especially interested to hear definitively from any Cox staff on the forum.

Thanks very much!