There's always optical media or SD cards with physical write-protect toggles. (If you leave the optical media in the writer, though, conceivably an absurdly specific virus could cause the device to burn out existing contents.)
The read/write switch on SD cards is 100% up to the reader device to honor or ignore (seriously)
The drive controller could strongly enforce the onceness of writes. Possibly by attempting a read before every write. Or if that's not enough, with independently articulated read and write heads, the write head's movement could be mechanically restricted...