Basically, if this game wants to correctly depict the time and place it wants to depict, bucklers should be inescapable, and yet from what I can tell there are none.
In essence, using pretty much any one-handed weapon on foot during this time period without anything in the offhand would’ve been rare, or even considered an outright bad idea. Therefore, everyone who carried a sword, a mace, an axe or anything like that probably should have at the very least a buckler too.
For example, there is no fencing manual documenting the use of an arming sword without a buckler or shield of some sort. It most likely just wasn’t considered a good idea. The closest thing to an exception would be some works about the Messer, but here we have to assume either that it was either covering a duel demanding identical weaponry, or some other rather specific context.
Messer and buckler is also covered in fencing manuals and was probably considered more far more effective than just having a Messer.
So who would’ve used a buckler?
Basically anyone with a one-handed weapon and no larger shield. Archers, polearm infantry, people just travelling from point A to point B, and so on. It was extremely popular.
The big advantage of the buckler is that it was convenient. You could carry it on your belt just like a sword without it being any hindrance to whatever else you are doing, and when you need it, you just grab it and you’re good to go.
tl;dr:
Sword and buckler is cool as hell, and was probably one of the most common weapon sets of the time. So where the hell are all the bucklers?