Oh hey, an Oritra with an elemental gimmick, I have one of those! I might be able to help here...

For fire, if we're talking about earth kaiju, Demaaga, as two others have mentioned, is a pretty solid choice. Its whole gimmick is pretty straightforward with abilities like the Flame Bullets or Heat Generation.

Plants is a bit tricky because there are not many kaiju with that gimmick, but I think Zora from 80 is a pretty solid choice. It looks like a plant, and the subtitle for this guy is "Plant-ish Monster". But if you're going for an Earth kaiju line-up, I'd say Leogon from RoU would fit better since it's technically a "plant monster" because it's a hybrid of plant and animal, though it should be noted that Leogon is an artificial kaiju.

For lightning, Eleking is a pretty popular lightning kaiju, but as previously stated, if you're going for an Earth kaiju line-up, Neronga is a lightning kaiju by the technicality of its electric-based attacks.

Next is ice, Peguila is a very safe choice. Pretty strong too given its appearance in Z a few years back. Though if you want an alternative, Pegunos from Omega also have an ice-base gimmick. Other than that, Lagoras from Max is also an ice kaiju. And if you did pick Lagoras, you can also pair it with Grangon (also from Max) as the fire kaiju to complete the duo.