are there weapons and armor with that characteristic? i have searched for hours through vendors but couldn't find anything.

Yes, as far as I know. It's possible that all "Magister's" stuff adds +1 to all magical skills. Also, there should be relics in the game adding +2 to all magical skills.

Yes, there are items which increase all magical skill by 1 point. I'm not quite sure if that's true for weapons but definitely for armor and jewelery.
(Every vendor randomly renews his proposal every time you start a new conversation with him/her so you only have to talk to one vendor until he/she has the items you look for.)

As far as I know (body) armors can only raise armor, attributs and resistances and not skills. Weapons also can only raise damage types, armor and resistances and not skills.
Only helmets, gloves, boots and jewelery can raise skills.