Try graphite lube. You might need to get the current grease out of the mechanism though?
Put the padlocks in some old socks or something over night. Heat the key up with a lighter before you insert it?
Even with the key in, the internals were frozen solid. Might try socks and a different grease. Not pissing about with lighters though, if it comes to that I'll get a fucking blowtorch.
Try graphite lube. You might need to get the current grease out of the mechanism though?
Put the padlocks in some old socks or something over night. Heat the key up with a lighter before you insert it?