Hey Natalie,
If you are looking for custom picture erotica, maybe we can work together. However, they will not be exclusive, as I'll post them on my site too. But they'll be free against a link back
Otherwise, here are a few links:
http://www.customeroticasource.com/ce/writers.shtml
http://www.wetwords.com/
http://www.soulgasm.com/customstories.htm
Another alternative maybe to go to
http://asstr.org and check out a few authors and contact them for quotes on custom/exclusive erotica.
Prices differ enormously between a good writer and a newbie writer... some will give it to you for free or 10 bucks, others might charge 50-200 bucks