I've found some decent bargains at UK car boots sales in the past, but now I think more people are clued up to collectables and listing things online. As AJ said it's slim pickings. But if your're persistent there may be some bargains still to be found.
But good luck with the Farthest From if you get chance to go, seems to be growing in popularity for the UK.
thevintagetoyadvertiser.org 1970s and 80s vintage toy ads and other retro paperworks
imperialgunnery.com Vintage Star Wars action figure weapons and accessories guide