Valar look like whatever they want to look like. Most choose to look similar to elves most of the time, even Melkor did.
D&D miniatures elementals could suffice for an appropriate Valar, but you aren't really getting a cabinet piece unless you heavily convert or preferably add it to a vignette.
You could have some elves making an offering to a Valar by taking some elf miniatures adding a large water or earth based miniature and posing them dramatically. Most Valar are friendly.
All the above miniatures are impressively big.