if you have a camera with xlr inputs or a audio recorder such as a Zoom h4n (the latter I'm guessing you don't have) then you can talk to whoever is managing sound and see if you can tap into the soundboard/mixer and essentially get the audio from the mic they're talking into. ... perhaps? I've never actually done this, I'm just basing this off the very little I somewhat know about audio.
but ya, if you don't have means to do that then I suggest picking up a lavalier mic like the person above me suggested. If you have a shotgun mic then that might get the job done as well depending on the situation.