Once you get past the peak time of August it becomes easier to find accommodation. There are plenty of hostals in Leon to cater for pilgrims walking the Camino de Santiago in summer. I've not been to Zamora but stayed once at a place called Hostal Bristol (I'm afraid I don't have their address or telephone number to hand) in Benavente (halfway between Zamora and Leon). Handily placed for visiting Portugal as well as Leon I can recommend Benavente. Some great free tapas in the bars.
Have fun, wherever you go!
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