Plenty of ways. Rather than just replenishing, you can buy Voiddust either off of the auction house or from one of the NPCs in various places in exchange for various currencies (Conquest Points, etc). Each Voiddust can be turned in for one stone.

Also the KIs needed are 100% despite what you say; it's not the ones dropped from the fight, it's the abyssite that you upgrade to get to the higher-tier fights. Once you beat each fight (except T1/3, where there's two fights each, as I recall) you talk to the NPC and ask them to examine your abyssite, and it upgrades. So no more than 12 fights, and if you buy dust to cover stones when you're out, you can finish in a day easily.