Shouldn't that be "gc_11_0_0_mes_2.bin" — without the double 0? That you could download from git.kernel.org among other places.
That video card came out around the same time as the current version of Debian stable, so it's probably too new to be included in your version of firmware-amd-graphics. It would go in /usr/lib/firmware/amdgpu/ with a bunch of similar-looking files. The other thing you might need to go with that firmware is a newer linux kernel, which you could get from backports.