Well, if you're in Qeynos a good place to look for Lead Clusters is in the Peat Bog. Look around for "Misty Stone"s, minign them gives you either Lead Clusters or Raw Malachites, bout an even chance of each in my experience. Don't bother hitting the "Murky Ore"s, they only give tin clusters.
The Misty Stones aren't too uncommon there, but people will snatch them up when they see them so you need to be a little bit lucky. Good luck!