take one with you to a hardware store and see what they got. apple would not have allen screws made just for them as its much cheaper to buy ones that are already out there. i'm sure you can find them.

the bottom front foot on mine has one of the screws stripped but very carefully and slowly I got it back on tight enough.
Mac mini C2D 1.83GHz - 2GB RAM - 200GB 7200rpm HD
Sawtooth w/G4 1GHz - 1GB RAM - SIIG SATA w/2x1TB HD
B&W w/G4 600MHz - 1GB RAM - 2x80GB HD
Sawtooth G4 400MHz - 512MB RAM - 40GB HD
Dell Ultrasharp 2007WFP 20" Widescreen LCD
2.94TB Total Storage