Man, I didn't think to check Amazon. I went on a little shopping tour yesterday and found some hobby pearls in the right size (2mm). They are the best I could do. But I think I will try these foam ball too as the pearls are not fully round. I'll have pics soon once I got the updates added.
For now this is the progress on the texturing.
I want to add that little wedge in the back that was used to control the angle of the barrel. And then I will try adding the pearls (or whatever I find suitable in the end).
Also I will make an easy version, if someone wants to equip his ship with 32 cannons and no time :-)