I was just wondering if there are any nice bucklers in the game (it's my second time I play and I've didn't find any this time either)

I can say in some confidence that the creators of Shadows of Amn have a lot to answer for once again. There are only Buclers +1 and that is it.

After the perfect job done on the first one i am surprised by the amount of loose ends and gaps in BG2

Harsh but fair i think.

I believe there's only one. It's a buckler +1 in Mae'var's guildhall.

There is also Kiel's Buckler from ToSC. It's not available normally in BG2 but you could use shadow keeper to give it to your character. It is a +1 buckler but it also gives a +1 boost to your dexterity, which, depending on your current dexterity could provide an aditional AC boost.