As I wrote "except for the film" and the films were a melting pot of illogical concepts or at least concepts that were totally contradicting the lore.
Besides these heavy amoured orcs don't fit the Edain concept of MM. They are meant to be a wild host of different creatures.
And even IF I would like the idea of MM orcs joining Saurons forces in Dol Guldur and getting armed there, WHY should they be available for MM. They would have left their kin to fight for Sauron.
Its not vice versa (heavy armoured orcs from DG moved to MM)
Greetings
Maraelion