I know Resurectra teaches GM Blaster (on the good side) if you have 10 skill points in the skill, but is there some other, hidden requirement for it?
Every time I go to her for training, she says that my characters don't meet the requirements, even though all of them has 10 points in the Blaster skill, and also their own blasters (everyone has at least one), though I guess the latter isn't even needed.
I even tried asking her for training after completing the game, and still no luck.

No, I didn't even know it functioned like other skills (I recall, but maybe mistakenly, that in MM6 you get to become a GM without earlier ranks in Ancient Weapons). Also, even a skill guide I checked said nothing about the other two.
Thanks, this solved the problem.