Although the old style terrestrial shops often have a limited range, all the old favourites are available online. Duck oil, GT85, Plusgas, 3 in 1, as well as the ubiquitous WD40. I bought one of each a couple of years ago to try them out. I think I'm finding Plusgas marginally better. 3 in 1 can be a bit sticky and actually increase friction in some circumstances. If you put it on a brass woodscrew and screw it into a block of wood it's very easy to snap the screw. I'm a bit disappointed with Loctite Freeze and Release which is quite expensive but doesn't seem to have any practical advantage over normal stuff when I've tried it.
I've also found Dinitrol can work wonders. Things that have got the thin and runny ML3125 on them have been surprisingly easy to undo, no matter how corroded they seem. I suppose what's needed is some sort of solvent and some sort of light oil, so mixtures of paraffin and thinners, diesel and acetone etc. are probably just as good.