Mazda 6 GH rear knuckle bushing replacement is a bit tricky due to not enough space there, but it is an absolutely possible DIY job and you can do it in your garage easily.
I'm not sure if there is a part number of that bushing. I think it's a part of the knuckle, so only aftermarket options are available. You can try to find them by the rear knuckle part number. In my case, it is GS1D-26-11XC (Mazda 6 GH 2011). I was able to find only Febest MZAB-114 bushing by the part number and some other local brands that are essentially the same, and this was what I installed that time. So far, so good.
