I am sorry that you have gone through this. The best way to find out would be to check the state's probate/family court where the marriage had jurisdiction or where one of you lived long enough to establish jurisdiction. He could have done a a divorce by publication or if you can't figure this out, perhaps you woudl like to have your divorce done by publication in PA. Your instinct is correct, finding out won't be so easy but try and pin point the logical places he would have or could have lived maybe even Vegas and check the courts. Take care and I wish you all the best.
Legal disclaimer: The response given is not intended to create, nor does it create an ongoing duty to respond to questions. The response does not form an attorney-client relationship, nor is it intended to be anything other than the educated opinion of the author. It should not be relied upon as legal advice. The response given is based upon the limited facts provided by the person asking the question. To the extent additional or different facts exist, the response might possibly change. Attorney is licensed to practice law only in the State of Massachusetts. Responses are based solely on Massachusetts law unless stated otherwise.