It's not the cheapest option, but I prefer to use IAS on any travel show I do.
http://www.professionalwireless.com/ias
I do a master coordination and then just plug in zip codes for all the dates on the itinerary.
It usually puts me about 98% in the ball park. I'll over-coordinate (If I have 10 mics, I tell IAS 14) so I have some wiggle room for the occasional bad freq in any given location.
I've used this method for several years now and it's made RF life on the road much simpler.
I also recently picked up a spectrum analyzer, but that's another thread...