My "California Region Railfan Timetable 11"
from Altamont Press lists the frequency
as 151.625 MHZ.
This would be from handheld radios during the Loading or Unloading of the Circus Train.
You would need to be within about 1 mile or so of the Circus Train loading location in order to hear these handheld radios.When the Circus Train out and running on the railroad the train uses the same RR dispatch frequency as any other trains on that Subdivbision. You can also find these frequencies using the appropriate Altamont Press Timetable for your region in the west.
Information on purchasing Railfan Timetables from Altamont Press can be found at this URL:
http://altamontpress.com/catalog/timetables.html
At the present time, ALtamont Press only publishes timetables for the Western half of the USA. I imagine Altamont Press will eventually cover the entire USA but we are not to that point yet with the growth of Altamont Press.
If you are not in the west then I would recommend joining a railfan group at http://www.egroups.com and asking if anyone knows the frequency for your section of railroad.
I hope this info helps you!