I never did get any support trying to get this to work. However, I did write about how I got it to install on my MBP after lots of work:

Thank you @hethi , I opted to remove command-not-found until there's an update to fix its behavior. For anyone who may come across this issue and would like to remove it:

Is there a workaround or manual way to fix this issue in the meantime?

Since I haven’t received a response yet:
I went ahead and installed PureOS inside a VM. Can someone on the dev team point me to the necessary repos to build a new live disc? I’d like to try to modify the ISO disc with the changes I need.
I think I need these, but not 100% sure:
https://source.puri.sm/pureos/infra/make-live
https://source.puri.sm/pureos/core/live-build

Would it be possible to add the nls_ascii module into initrd on the install disc? If so, I may be able to install on my MBP much more easily.