I would like to know this too. Can anyone help?
I am using Minecraft Forge, so I'll check if it can help me.
I couldn't find one that supported metadata so I made one.
(I'm just learning too so there might be a better way.)
Create a new class named WorldGenMeta and copy everything from WorldGenMinable into it.
make these changes to the first few lines:
public class WorldGenMeta extends WorldGenerator
private int minableBlockId;
private int numberOfBlocks;
private int minableMetaId;
public WorldGenMeta(int i, int j, k)
minableBlockId = i;
minableMetaId = j;
numberOfBlocks = k;