When I get some bandwidth I want to do something on codes in the K through 12 classroom. You start with simple table-based codes to have some fun with numbers and letters (and to get some practice using tables), then you build on the concept over the years, introducing problem solving, probability, even number theory (public key codes) and programming.
With that in mind I Googled cryptogram maker and got this. I didn't look at the rest of the site so I can't vouch for it but the cryptogram maker did most of what I wanted it to.
3 hours ago