They are either #8 or #10 screws. Available in local hardware store. Make sure they are not too long. If #10, make sure they are the proper thread (coarse vs fine)
One idea that I heard was to replace the screws with allen bolts. Easier to start in the hole and less chance of dropping them.
Paul, if I remember, he is in Portugal and I doubt local hardware stores there carry scads of S.A.E. hardware. Their stock is probably all metric.
Mikhett, I can remember seeing some time back one of the resto parts suppliers offered them in a set. I think it was Concours Parts in Nevada, but not sure. Could have been Mac's.