The only place I would think you could get the bezel or insert would be Omega
I am not sure they would sell you the part for a watch it’s not supposed to be on. It would fit (assuming you mean the 300 SM Master Chronometer) and I think it would be a good mod but not sure Omega or an approved repair would supply the part. The click spring / detention would also need to be changed I would have thought, the spectre has a bi directional bezel.