The league, which includes six teams, begins play on Oct. 8. Each team has a roster of 35 players.
Robles is the highest rated prospect the Mets are sending. The 23-year-old right-hander is ranked No. 20 on MLB.com's list of the Mets' Top 20 Prospects.
He's spent this season with the Gulf Coast League Mets and Class A St. Lucie, where he's currently 5-4 with a 3.99 ERA in 15 games, 14 of them starts.
Bradford, 24, is currently pitching for Double-A Binghamton and has a 3-1 record and 0.42 ERA in 17 relief appearances. He has allowed 15 hits in 21 2/3 innings. Bradford began the season with St. Lucie, where he was 6-2 with a 3.71 ERA.
The Mets drafted Bradford in the 35th round of the 2011 First-Year Player Draft out of the University of Central Florida.
Vaughn, 24, has played with the GCL Mets, St. Lucie and Binghamton this season. In 65 Double-A games, he's hitting .277 with nine home runs and 49 RBIs. The Mets drafted Vaughn in the fourth round of the 2010 Draft. The Phillies drafted him in the 43rd round in 2007, but he decided to attend San Diego State.
Maron, 22, has spent all of this season with St. Lucie. In 81 games, the catcher is hitting .230 with no home runs and 28 RBIs over 81 games. He has a .325 on-base percentage. Maron was drafted in the 34th round of the 2009 Draft out of Hicksville (N.Y.) High School.
Rodriguez, 21, has played in 62 games with St. Lucie this season. He's hitting .260 with nine home runs and 41 RBIs.
Chris Iseman is an associate reporter for MLB.com. This story was not subject to the approval of Major League Baseball or its clubs.