a simple way could be to name them all the same thing, and use VCE to give that named brick (which is actually several named bricks) a random chance of gaining a variable (with a diceroll, like aromania mentioned), and if that variable is true I guess, then make it do acheck that adds the item
but I dunno how to make sure it only spawns on one brick, or how to make sure it spawns on at least one
besides that, it's probably a really bad way to do it lol
and I'm really not sure if what I said would even work, I'd have to mess around in the game to really get you some definite stuff, which I'm probably not going to do at this hour
I'm not sure if the event to spawn an item on a brick is default or not, but I know VCE isn't (although, imo, it should be, especially since he's added other player-made addons), so you'll have to get that