Ah, I used to think as you do. Huge story arcs peopled with as many interesting characters as I could shoe-pastry horn in. All I needed was an artist (and to actually write the thing). Alas, whilst widely regarded as subordinate to the writer (at least by writers), artists have other ideas and insist upon believing that they shouldn't waste their talent on untested noobs. I know, this makes no sense, but still - that's the way it is.
The best thing to do is start small, writing one-off 5-8 page scripts for the Small Press (FQP or Paragon, for example) or any one of the magnificent projects gracing this very forum (hallowscream, Dr WTF?! and so on). Once you get a few things published, those pesky artists may start to take note and then you can start planning your mega-epic.
That's my two penn'orth, anyway.