[torgoguys]

Using an SD card (or micro SD in an adapter) connected to a USB reader might meet your needs. You can then use the SD write protect switch.

[jhallenworld]

I thing I learned only recently is that the write protect switch on the SD card is not an electrical switch connected to anything in the SD card itself: it just hits a lever in the SD socket that opens a contact closure and it's up to the system (hardware and software both) to bother to look at it. So on many systems the write protect switch doesn't even work.