I miss screws to fix a PCI board in my PC, however I can't find out what type of screw it is. Any hints?
Example of a screw assortment of suitable screws. Better hardware and DIY centres may also carry them. A local PC retailer may give you a single one if you are ask nicely.
Note: 6-32 is a US-style screw sizing, so it may not be as readily available from hardware stores in Europe. Don't try to force a M3 screw as a poor substitution, the thread pitch is wrong.
There are alternatives to trying to get the correct screw specification.
When you buy a case, you typically get WAY too many of a large assortment of fasteners. Therefore, anyone in your area who deals in computers (almost in any capacity) will have more of them than they know what to do with.
You can also often scrounge one or two from your existing case from a less vital location as a temporary measure.
If you are absolutely "in the middle of nowhere", you can ask someone to send you some - surely someone can pop a few into an envelope for just a few pennies - postage will, no doubt, cost more than the value of the screws.