According to Official Guinness Records,
The most 3-point shots made in an NBA quarter by a team is 11 by the Cleveland Cavaliers against the Los Angeles Clippers (both USA) on 31 January 2010. The Cavaliers won the game 114-89. The 11 3-pointers helped Cleveland score 46 points in the opening frame. This ties the previous record of 11 set by the Milwaukee Bucks on 28 March 2006.
For a complete list of 2010 records, please visit 2010 Guinness Records in United States.