Typically there will be a court ordered legal name change. If you area aware of where the person was living at the time (or can speak with the person) you can obtain at least the name and location of the court and the case number. Legal name changes are for more than transgendered / transexuals, however as medical information would be included for these name changes you will find those records sealed.
An alternate method of showing the two names is to learn which local newspaper publishes 'legals' for the court system. That legal announcement will have the two names, the name of the court, and case number.