Earth Ele slayers work on any of the elementals brought up by a gargoyle pickaxe, as well as the Shadow Iron elementals in the Yomostu Mines. However, because persons working as developers during the period that garg picks were introduced didn't bother recoding the Dull Copper Elementals (because they didn't come from the GPA), they are unaffected. The DC eles can be found in Shame, the south side of Compassion Desert, and the Sorceror's dungeon (the first two in Tram & Fel, the 3rd in Ilshenar next to the Valor-area Champ spawn)
The Snow elemental slayer works on Ice elementals as well, as of a change that occurred about 3 years ago (can't remember the exact publish). I have a high-leeches, 25% SSI longsword that's a snow slayer that I use on the rare occasions I go the lady of the snow area, because I 1-2 hit kill the snow and ice eles with it, and it does enough damage against the (undead) lady of the snow that I get better Damage over Time PLUS great chunks of health and mana back against her, without losing the ability to quickly kill any ele that jumps into the fight.