Some of the best rectifiers can be salvaged from old semiconductor
furnaces from a university research lab. Quite a few furnaces are
coming of age to be disposed. Industry donated them 20 years ago.
Universities run them until the central heating element burns open.
This usually leaves the power controller intact with six high power
rectifiers (two for each half-wave x 3-phase).
If you provide a specification on what you need, then I can keep an
eye out for you.