There are many typewriters, even portables, that are missing cases or have case too badly damaged to serve their original purpose of protecting the machine. The most common solution in a case rehab or to find a good case with a parts machine and use the good case for the good machine.
It’s difficult to find new cases that will work for a typewriter because most cases have sections (lid and base) that aren’t proportioned similarly to a typewriter case. However, there is one category of available cases that some times have shallow and deep sections like a typewriter case: snare drum cases. Only some of the new ones would be suitable to be repurposed for typewriters. one advantage is that they are sized appropriately, being generally square and able to contain a 14″ diameter 5-6″ tall drum. This is slightly roomy for most portables. Padding or transferring the hardware from an old case will take some ingenuity. There are even some cases for deeper drums, toms and marching snares, that might fit full-size/office machines.
For ultra portables there is another left-field option, cases designed to hold LPs. There are several with dual, sometimes locking, latches and they come in a small variety of colors. LPs in sleeves are ~12.5×12.5″, so the machine would need to be a bit smaller in order to leave room for some padding.