Ice Paraelemental from WotC's Chainmail line.
The
Fire Elemental or
Ice Elemental from WotC's D&D minis line.
Reaper's Fire Elemental.
Dark Age's
Ice Elemental.
Of course this guy is armed with an Azoghar, so you'll need to put one of those in his hands. Most of those being molded in clear resin or plastic (the Dark Age has an optional pewter version) would make it difficult for modifications. Also some of them may be larger than a size 3 model. I know the Dark Age Ice Elemental is.
Another possibility is to use the Golem of Darkness and just paint him different colors. Firey Red for a Golem of Flame, Icey Blue for a Golem of Ice, Black for a Golem of the Void, and something different than the whatever you paint your Golem of Darkness to be the Golem of Discord.
Another possibility is to use the plastic Nepharites from Blood Berets and Seige of the Citadels. They're a bit small compared to the Warzone Nepharites but are armed with an Azoghar. And you can use the gun on the Blood Berets Nepharite as his Incendiary Bellows.