I am sorry to learn of this situation.
Unfortunately you need a lot more information before you can viably set about starting a quiet title action. You state that you do not believe that the bank has sufficient documentation to support their lien, but you do not know what documentation they do have, and you do not have any information regarding what documentation or contract that your ex wife actually entered into.
Before initiating a quiet title action (which is a very complex form of civil litigation, and you really should hire an attorney to represent you in - these are procedurally driven lawsuits and even small missteps in procedure can cause you to lose even a viable case), I would recommend trying to get more information from the bank regarding the loan and what information you do have. I am sure you have already tried doing at least some of this, but working with their "back office" (usually customer support in Chatsworth), you can get more information on your loan.
The Fair Lending Act can help you if you run into problems (it requires the lender to be transparent when dealing with you), and make sure to use "confirmation letters" to follow up with phone calls - it is a good way to document your efforts to communicate with someone. Confirmation letters: Keep written records of all communications - so if you speak to someone by phone, promptly send a follow up "confirmation letter" summarizing your conversation, who you spoke to, when, and any agreements you reached. Keep copies of your outgoing correspondence, as well as anything that you receive.
If you do find that you have a good basis to file your quiet title action, You can find local civil litigation attorneys using the State and local Bar Association directories, or private directories such as www.AVVO.com; www.FindLaw.com; or www.Martindale.com (I personally find www.AVVO.com to be the most user friendly).