Most decent hardware stores have a section somewhere full of little bins with screws, bolts, nuts, and other misc. do-dads. The good stores have a really big section of bins, and they've often got some with screws. In the US, I have good luck with ACE stores, and lousy luck with Home Depot. Can't tell you which stores to hit in Europe, but the general rule is, you want a store that's selling to farmers, mechanics, and the like, rather than stores that market to yuppies wanting to fix-up their house.