I have seen many references in the rule book to duel wielding, but I can't find any pages that actually address rules pertaining to it. If you for example wield a spear in your main hand a quarterstaff in your off-hand, do you get to use two rolls for attacks?

There is a card that's called "Dual Strike" or somesuch, and that's the way to go if you want to wield two weapons. But you can't attack twice with your basic attack card, or any other attacks for that matter.

The Dual Strike card has been changed in the errata too, so you can download the card on the support page for WFRP to get the updated rules on it.

Anyone may hold a weapon in each hand. You need to purchase specific dual-wield action cards, such as the previously mentioned Dual Strike, to be able to strike with both weapons using a single action. Otherwise, you strike with one or the other (not both) when you use the action card.

Also, I would be hesitant to let someone dual wield a quarter staff and a spear. Sword/Sword, or sword/dagger, or Axe/Hammer, but that combination takes definitely one, possibly two two-handed weapons, but one held in each hand...

if i am not wrong there s a weapon type called main gauche (or something like that heheh) which is a hand weapon type for your off hand