BCN Envoy availability is always blocked by US Airways - that is their way of sticking it to their own elite flyers. Those seats will open up closer to the flight time. I travelled that route several times doing either upgrade to Envoy or award Envoy, and this was the case for at least past 3 years.
It takes strong nerves and daily calls - but more than 30 days out - they keep the seats to themselves.
In addition they also play defense in committing the airplanes - which dictates how many seats they offer.
If you believe in unassigned seats in Envoy - you need to reconsider - just buy more seat than you see - you can always cancel within 24 hours ;-)