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.