They operate on CSX freq's. Your best bet is to enter the "ex-RF&P" channels. I was recently down there last week and will be again on the 16thish.
Later tonight I will post the freq's that I use.
Currently there is a MOW curfew in effect during the day between Rocky Mount NC and Richmond, so you will see very little between those two spots, and limited running between DC and Richmond. Around 4pm, expect to see a whole bunch of trains running from 4pm to 6am until the maintence people start work again.