This is the Official Opening Day Roster released by 2K Sports for MLB2K12 dated April 3, 2012.
File is in .rar form. Extract or unzip it to your 'Saves' folder. Filepaths for Windows Operating Systems are as follows:
For WinXP users: C: / Documents and Settings / %UserName% / Application Data / 2K Sports / Major League Baseball 2K12 / Saves
For Vista and Windows 7 users: C: / Users / %UserName% / AppData / Roaming / 2K Sports / Major League Baseball 2K12Saves
Note: A few real-life players still have fake names because they had still yet to appear in a Major League game when this roster was released. Examples include Yu Darvish (Yar Devine), Yoenis Cespedes (Yonder Cervelli), and Freddy Galvis (Fernando Gonzales).