Kate Beckett (Stana Katic), now a Special Investigator for the US Attorney General, carries what appears to be a SIG-Sauer P229R as her sidearm. Other agents carry this pistol as well.
In "Number One Fan" (S6E04), Emma Riggs (Alicia Lagano) is seen with what appears to be a Tanfoglio TZ-75 "Series 88" that was imported by F.I.E. into the United States.
Shotguns
Mossberg 500
A government agent carries a Mossberg 500 12 gauge shotgun during a raid in Season 6's premiere "Valkyrie" (S6E01).
Browning Auto-5
In Season 6's finale "For Better or Worse" (S6E23), the leader of a biker gang wields a cut down Browning Auto-5 with a "mare's leg" style sawed-off stock & barrel. This shotgun is similar to the one used by Chuck Norris in the film Lone Wolf McQuade.
Submachine Guns
Heckler & Koch MP5A3
In Season 6's finale "For Better or Worse" (S6E23), another weapon used by bikers is the Heckler & Koch MP5A3.
Heckler & Koch MP5K
In Season 6's finale "For Better or Worse" (S6E23), another weapon used by bikers is the Heckler & Koch MP5K submachine gun.