I've run into this issue before in Missouri. Even if the wife waves their rights to the property, you still have to have the wife sign a quit claim deed. It seems redundant to me, but that is how we roll in MO!
Was a title company involved when the special warranty deed was transferred to you? They should have disclosed the cloud on the title in the title search, however, since it was a special warranty deed, the second title company is only responsible for the transaction between you and the broker.
As a general rule, I would never accept a special warranty deed. It should always be a warranty deed. My guess is that no title company was used for the original transaction. I'm surprised that a mortgage broker would accept a special warranty deed.
Regardless, you are stuck in this mess. The best thing to do is get a title lawyer on the case to find the ex wife. If you were using a local title company, they should be able to help you find a good lawyer that specializes in this. If not, I can recommend a good one.
Hope this helps.