If records have been destroyed you cannot provide them. This is more of an immigration type question than a criminal defense type question. I believe that if you have had your records destroyed then you would not have to provide copies of them. I also believe that if you explained this on the application that should suffice. However, I would contact an immigration attorney and find out exactly what is required. I would also attempt to contact the attorney I hired to get the records expunged to see if he has a copy of the expunction. I would also look closely at the question and see if it requires disclosing cases that did not result in convictions or cases that were obtained as a juvenile. If you were only arrested and not convicted it may be that you do not need to disclose this item. Call an immigration attorney to be certain.
Your best bet is to get a copy of the Petition to Expunge. That is the paperwork your attorney filed at the time of the expungement hearing. There should be an order attached to it that grants the expungement, and should serve as proof that you can no longer find the record. Call the Dallas County clerks office at 214-653-7009. Ask to speak to the section that deals with sealing records or the juvenile section. If you go down there, they can give you a certified copy. Another option is to contact the attorney who represented you to see if they have a copy.