I'm sure that someone will accuse me of SPAMming even though the
original question asked specifically about a spray lube to keep locks
working... so, here goes

The locks probably have some rust or corrosion in the mechanism
causing the problem.

http://www.amsoil.com/redirect.cgi?zo=1690163&page=storefront/amh

This is a spray that goes on wet and liquid carrier drys leaving a wax
like lubricant.  Motorcycle owners use it on the chain.  It won't
sling off after it dries and won't attract dirt..  It also displaces
water and silences squeaks.  It protects exposed metal surfaces from
the damaging effects of salt, moisture or chemical corrosion.

Please click on the link for a complete explanation.

Anything liquid will gel, thicken, stiffen whatever you wish to calls it
when temps fall. WD40, contrary to popular belief is NOT a lube. It is a
water displacer. Does that give you a clue? You must get rid of the water.
Try a dry graphite powder. You can get it in a regular can or in a spray
can. Works fine on my snowblower at temps down to -40. I don't do snow at
temps any colder and only did it once at that temp but the chute would pivot
with no effort... Hope this helps.
DaveD