I checked 3 of the listed participating stations and none of them listed a specific frequency.
http://gx4crc.com/imd-stations/Obviously, that makes sense since no one owns a frequency and they all can't be on the same frequency.
On the day of participation, check the various DX clusters to see if a particular frequency and station have been spotted. Like chasing DX the old fashion way, looked for lots of activity and/or pileups on a frequency.