Our good friend Ron perron in Maryland shared the following excellent frequency list with the Scan-DC listserv. Thanks for sharing Ron!
Potomac Consolidated Terminal Radar Approach Control
Washington Dulles International Airport (Shenandoah Sector)
118.675 / 257.875 PCT KIAD - LURAY
120.450 / 343.775 PCT KIAD - West Arrival MANNE
123.825 / 254.250 PCT KIAD - BUFFR (Also Westminster 5 Arrival into BWI)
124.650 / 343.775 PCT KIAD - South Arrival BARIN
125.050 / 350.200 PCT KIAD - North Departure ASPER
125.800 / 343.775 PCT KIAD - Final East IADFE
126.100 / 338.250 PCT KIAD - North Arrival MULRR
126.650 / 350.200 PCT KIAD - TILLY
126.825 / 239.025 PCT KIAD - LUCKE
134.200 / 343.775 PCT KIAD - Final West IADFW
135.775 / 343.775 PCT KIAD - North/Northwest Approaches, Southern Departures RCOLA
Washington National Airport (Mount Vernon Sector)
118.300 / 306.300 PCT KDCA - Final East DCAFE
118.950 / 257.200 PCT KDCA - West 9500'& below TYSON
119.300 / 335.500 PCT KDCA - Approach ADWAR
119.850 / 322.300 PCT KDCA - West QJAAY
121.050 / 343.700 PCT KDCA - West 10,000' up to FL 230 FLUKY
124.000 / 279.575 PCT KDCA - Andrews for Arlington Flybys ADWFR
124.200 / 269.000 PCT KDCA - East ENSUE
124.700 / 338.200 PCT KDCA - Final West DCAFW
125.650 / 348.725 PCT KDCA - East 9500' & below KRANT
126.550 / 269.500 PCT KDCA - East 10,000' up to FL 190 DAILY
128.350 / 270.275 PCT KDCA - South East 19,000' down TO 3000' DEALE
Andrews Air Force Base
119.300 / 335.500 PCT KADW - Arrival
125.650 / 348.725 PCT KADW - Departure
124.000 / 279.575 PCT KADW - Discrete for Arlington Cemetery Fly-bys