Are there any other nearby hotels? You could find one that offers a good rate and make that booking as a backup. Then, I'd call the hotel directly and ask them what's up. If you have a travel agent that you know well, you might even have them do it and see what the result is.

Yes, it is shady for the hotel to block all of the rooms out for every weekend. But I 'spose they have a right to do it: they are gambling that the upside of that one concert weekend will be bigger than the lost revenue from people who want to visit that city for other reasons on all of those other weekends and have now made their bookings elsewhere.

Two years ago, I went to a Packer game at Lambeau. I made my booking at the Hampton Inn near the stadium within MINUTES of the NFL schedules being released. I got my room for $64/nt., but my buddy who waited 1 day couldn't get anything under $125 for a similar-quality hotel. I've never heard of a hotel simply refusing to sell any rooms until it knows when all of the season's special events will be.