There is really no cause of action against the park that requested the information although, theoretically, if they then distributed the material that they illegally obtained there might be a cause of action for that.
You could likely sue the USPS for revealing the information assuming that you could prove that they provided information as opposed to the company finding out some other way.
As I mentioned in the other response, it is going to be hard to find an attorney that will take the case on a %, you are probably going to have to pay them by the hour or a fee to get them to take the case.
However, if you win your case you can ask that the other side repay you for the attorney's fees you already paid.
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