In addition to the Department's standard (D)Net, (D)Tac, and Common channels, try:
DHS Aviation and Marine Operations
FM:
168.8375 $293 Air 1
168.9625 $293 Air 2
169.2625 $293 Air 3
169.1625 $293 Air 4
169.3875 $293 Air 5 / Boat 2
163.4500 $293 Air 6
166.8875 Air 7
166.7875 Air 8
163.4750 Air 9
169.6375 Boat 1
AM:
120.4250 Tac 1
120.4500 Tac 2
120.4750 Tac 3
137.9000 "Company"
350.0250 Guardian Ops
136.7500 Ops
282.4250 Blue 1
308.3500 Blue 2
376.0750 Blue 4
136.3750 old air-to-air
123.0250 Helicopter common (news, MedEvac, government, etc.)
There are a handful more (in both AM and FM) that I haven't been able to confirm, but the above list from my notes should be a good starting point.