Mark,
Most Virginia MEDEVAC are shown on the various open source flight tracking programs by their aircraft registration or "N number". Their radio callsign is different. Here is my list and it is current:
Callsign, Base, Registration, Type, Mode S Hex
PHI
Aircare 1, Manassas, N305PH, EC135. A33332
Aircare 2, Fredericksburg/Shannon, N427P, B407. A516E5
Aircare 3, Leesburg Executive, N324PH, EC135, A37E79
Aircare 4, Front Royal, N302PH, EC135, A3280D
Aircare 5, Staunton, Shenandoah Valley, N385PH, EC135, A46F2A
Aircare 6, Culpeper, N431P, B407, A5281A
Centra One, Lynchburg, N390PH, EC135, A48416
VCU
LifeEvac 1, Hanover, N105NK, EC145, A0187D
LifeEvac 3, West Point, N730MT, EC135, A9CC30
LifeEvac 4, Southside Medical Center, Petersburg, N119MT, EC135, A04EC7
VSP
MedFlight XX, Chesterfield Richmond Executive, N28VA, B412EPi, A2CD7E
MedFlight XX, Chesterfield Richmond Executive, N71VA, B407GX, A97B90
MedFlight XX, Abingdon, N39VA, EC145, A4824C
UVA
Pegasus, Charlottesville-Albermarle Airport, N5UV, AW109, A63714
Sentara Norfolk
Nightingale, Sentara Norfolk General Hospital, N145NG, EC145, A0B676
Carillion Clinic
LifeGuard XX, Roanoke, N135WL, EC135, A48416
LifeGuard XX, Blackburg? N135VV, EC135, A08FB3
LifeGuard XX, Lexington?, N135LX, EC135, A08ED4
AirLife Virginia
AirLife, Martinsville, N136VA, EC135, A09357
Let me know if you want DC, MD and NC.
I hope this helps.