If you guaranteed your reservation with a credit card, request that they need to find you a replacement room nearby - if you didn't show up, you know that they would charge you! Complain up the chain of command until you get satisfaction.
I agree with several of the previous comments - this sounds fishy. They should be working more proactively to get a room for you.
For future reference, this is why it's good to book either directly through the hotel or with their loyalty program and guarantee with a credit card (and maybe you did) - more leverage than dealing with a third-party aggregator. Also, arrive early so that the "unavailable" rooms become someone else's problem.
All else fails, be sure to leave a scathing review online.
If you are really stuck, try Carlisle or Lancaster - both are about 40 minutes from the fairgrounds, much cheaper, and probably have plenty of rooms.
I hope that LaQuinta comes through for you or that you stick it to them good.
