This one is a complicated Question to ask. Because there are a few Problems to solve for.
You will have to load all Chunks in an Area and do a scan of all GT6 TileEntities to find out where the Ores are. It is not really all that possible to do it any other way, if you want it to be reliable, since Caves, Dirt and the World-Height-Map exist to reduce total Ore Count. Not to mention that a few Stone Layers that are too flat to generate Ores exist as well even if rare.
One could do a simulated run of the Stone Layer Generator to see what Veins are most likely to exist where and then go to the places you need and check if those Veins exist. But that would involve writing an Addon Mod.
A Suggestion I would give to early Players is to just go next to a Desert and harvest Small Ores from that, since it will net you most of the Ores you need early on, without having to care much about Veins.