Write to the prison system and request your files under the Freedom of Information Act. There are a number of websites that explain the process and give simple examples of these letters. You may be expected to pay a minimal fee for copying. You are entitled to copies of the files.
Write the to Bureau of Prisons and request them. There is a special form and you may have to have your signature notarized. The Freedom of Information Act applies and you should be able to get your records. It may be beneficial to call first.