From the Model Mayhem FAQ:

How do I find the Sponsored Casting Call I just posted?
You can always find your casting from My Stuff > Manage Castings.

If you want to find your casting from the casting search page, click on the casting/notice link at the top of the page, and enter the search terms that match your casting. Your casting will appear as one of the three pinned results, and will appear at random during the review of the search results.

Please note that this randomness is designed to give all sponsored castings a fair chance of being viewed.

If you still can’t find your casting call, please email Customer Service and we will be glad to help you find it.