Okay, news here.
I was able to find a WWII Magazine Safety at a gun store 50km from where I live.I just mounted it and discovered that the problem was not only caused by the bent magazine safety: the slide is also a little worn in the point where the mag safety hits.Problem not fixed yet. My gunsmith suggested me to heat up the mag safety and slightly bend it towards the slide. You think it might work? I don't want to change the slide, it's very hard, legally speaking, to buy one in Italy as it's like buying a new gun and it would compromise my Mauser authenticity.