There is a spawn in Edgeville Dungeon near the Varrock entrance. It can be reached by using the Edgeville entrance south of Edgeville bank To be more precise:
Head due south of the Edgeville Bank, until you see a trapdoor inside the ruins. Head north until you can go no further, head west until you reach Vannaka, then follow one of the paths until you see hobgoblins, run through them and north, until you see the zombies/skeletons. Note: If you see Hill Giants, you went too far. Right there on the ground is your key! Now head up the ladder, and leave.