Have you tried spraying lube in the lock. I've used WD-40 successfully but your locksmith probably has a lube specifically for locks.
I use powdered graphite to keep locks lubricated. Works great. Not sure it will free up a stuck lock though.
JPRB
I use PB Blaster.
I buy it from Crest Ind. but I'm sure you can probably get it at Lowes or Home Depot.
It works when WD40 doesn't.