Most balloonist have there own collection of frequencies, and not always the right ones
Your best bet to listen is to get a scanner, Especially one the covers air band, (After all these are really aircraft and should have one on board.) Alternatively you will need to contact the owner/club. If you have time try chasing the balloon to the landing point. along the way you will see a chase vehicle. ( watch for the trailer ... this is a great way to spend a early morning.) if the have radios they will normally be happy to give you their freq's.. they probably won't know off hand, but will find out for you anyway.