Go along to your nearest computer repair shop and ask them to sell you a few. They'll know the thread size and length pan head screws that you need. They are a standard size for most equipment and shouldn't cost you more than a few pence
http://www.modelfixings.co.uk/fixings.htm
This company supplied screws for my telescopic sight mounting.I tried all over the world nearly to get them from optics suppliers including Steyr who made the optics attachment I was repairing.