You could most likely find what you want in a 3rd-party product, but otherwise, you'd just have to stick with a Sorcerer or similar caster who only chooses to learn elemental spells but who is not technically limited to them.
Also, you might join the Cydra group on the Yahoo! website. The Jester, an awesome poster around here, has a lot of his Cydra campaign material available for download on that Yahoo! group, and I'm one of the various folks that joined the group to see his work. The Jester has a custom Elementalist core class in one of his Cydra group documents, that he's used for quite a while in his campaigns. It is purely an elemental magic-user, AFAIK (though it's been a few years I think since I read it).
Other than that, if nothing else you could just houserule the Shugenja to have access to all 4 elements, in exchange for losing their Element Focus benefit, and their shugenja school (I think they're called shugenja Orders in Complete Divine, unlike Oriental Adventures, like Order of the Gentle Rain instead of the OA version, the Kitsu School). That would probably, I suppose, be sufficient to balance out the benefit of access to all four elements instead of just three.