Well I think that
>green ones should only be dropped by creepers
>gold ones should be found in dungeons
>blue ones, hmm. smething to do with water
>red ones to be crafted out of flint and a lava bucket in a jukebox style (lava bucket with flint surrounding it, sacrifices the bucket in the process)
>greyscales (white grey and black) could possibly be found in random chests in caves
>orange could be found in random chests in the nether
and I'm out of ideas :c