I have never seen too many surplus stores, the ones I did come across were more "Dollar Store" type stores; great places to find CA glue for €0,50 but that's about it.

I do happen to live about two kilometres from one of Europe's largest army surplus stores. Needless to say, half my clothes are form there (I am quite a minimalist). They're not terribly cheap, but in general they have decent prices for great stuff.

Best finds would probably be boots in great condition: a pair of low Swiss army boots and a pair of Czech motorcycle boots (perfect for winters with loads of snow and/or slush), both from the 1980's, both under €30. A bit of elbow and leather grease, a few stitches that needed to be fortified and good as new. My local cobbler/shoemaker was impressed too. Both pairs will outlast me.

Oh, and wool. Lots of wool. I love wool. Wool, wool, wool, there it goes, into my clothes.