I had a hard time finding any information myself regarding Naginata instructors in Portugal. I found an international organization that listed on in France:
I also know that the Bujinkan have two schools in Portugal, but I don't know for sure if they teach Naginata. Probably Sai also.
It has been recommended to me several times by many black belts to NOT cross train until I have a firm grasp on my shodan in aikido. I'm inclined to agree with that idea. Aikido is good and will help you learn ukemi as well as to protect yourself in other ways when practicing martial arts. Weapons training is fun, but how often do you find yourself walking around in the public with a naginata or sai or katana? It just doesn't happen. Learn to defend yourself with empty hands and then work your way up with the other stuff.
Aikido does use bokken, but so much of what we do is based on the sword. By the time you go to learn weapons full-time, you'll be well grounded.
BUT... if you really want to know more about those weapons, I would contact either that French school regarding naginata or the Bujinkan. From all I have read about the Bujinkan, they have a good reputation and their Soke is legitamite and well respected around the world.
Good luck to you... but keep on training!