In Fate/Zero Lancer is using a fighting style with 2 spears, one in each hand. After doing some research, I couldn't find any similar fighting style in real life.
Is there such a fighting style using a spear in each hand in real life, or did the creators of Fate/Zero make that up?
There is in fact a style of fighting which utilizes two spears. The Irish used to use single-handed spear combat. This style of fighting was used only by those who already had great skill in double-handed spear combat due to the requirement for greater control and strength.
In this style of fighting, one would carry a one-handed spear in their strong hand, and either a large shield or a small shield and spare spear in their right. While the combat style wasn't specifically designed for fighting with both spears at once, this is clearly where the inspiration for the movements of the character are derived. Some of the ways he strikes in the show even have great visual resemblance to this fighting style.
Add that to the fact that his character is of Irish legend, one of the most famous knights of Fiana, and that within those legends, he does have two spears among his collection of mythical weapons, it leaves little doubt that our Irish, spear wielding combatant would be using Irish single-handed spear combat.
There is no such thing as dual wielding spears in the world of martial arts. This is mainly due to the reason that it is plain impractical. Swords already have their disadvantages when dual wielded. But with spears, it would be close to impossible to have a proper fighting style unless you would only fight against other dual spear wielders.
Dual wielding is the technique of utilizing two weapons, one in each hand, during combat. It is not a common combat practice, since it does not offer much advantage. Although historical records of dual wielding in war is limited, there are numerous weapon-based martial arts that involve the use of a pair of weapons. - Wikipedia
Even though it is unpractical in real life situations, it is commonly used in anime and the likes, as stated on TvTropes:
Dual wielding appears in various Real Life cultures and combat styles, but it tends to be over-represented in fiction because it's... well... cool.
