The remote control is called RC-946S. Whether it can be bought separately is beyond my knowledge (a quick search on Amazon or here at digitec does not yield any results).

Alternatives are the Logitech Harmony or similar.

By the way: I also own the amplifier for the home office, but I rarely use the remote control and operate the device 99% via the iPhone or iPad. I find it much easier to use when searching for an internet radio station or streaming music from Apple Music ...