Frankly, you won't find much, fighting with two weapons is almost always a bad tactic. A one-handed weapon with a shield, or a larger two handed weapon, is almost always better. The only example I can think of a rapier + a dagger used together. You can also look into lantern shields for a bit of fun.
Whenever a fighter had two hands to fight with, he generally selected a two-handed weapon, not two separate weapons. The only real exception is in dueling where they had specific rules and modes of conduct.
Does he have to use the two weapons simultaneously or can he use them in succession? Many Medieval soldiers had a back up weapon in case they lost their primary. Archers usually carried a dagger. Knights had both lance and sword.
With a buckler, I would use a spear. However, I guess it would precipitate amusing dialogue with two handguns. As to how he uses them, he uses them one after another (he uses a chinese and irish fighting styles).