It looks like ordinary encoder without push switch. There is a good chance any standard encoder would do.
Just get one that has same thread and shaft type and length, mount it with nut and connect it with wires to PCB. Of course it has to have enough space behind the PCB for it to fit.
Getting original is not going to be easy, and these were not sold as parts ever, only whole PCB as subassembly.
If you get a good quality encoder, chances are it is going to last longer than original one.