Take it to any shop that sells and mounts scopes, and either they will have some to sell you, or they will hand you a tray containing about a thousand different screws they have accumulated, and will tell you to sort out the ones that you can use.
Like as not, they are a finer thread pitch than the usual hardware store variety screws, so you are pretty much stuck dealing with firearms related sources.
Talk nice to Leupold on the phone and they might just slip a couple into the mail.
Cheers
Trev