Except non is not an english word, it is a prefix of latin origin For more, including variants, see wikipedia Which is why american style manuals will always ask you to merge it with the subsequent word, without a hyphen
For someone looking to avoid it, what are some good alternatives Onelook dictionary search doesn't show much about We need to be aware of our blind spots to make sure a
I'd use the two hyphens. The answer above is the valid answer, just one word Nonexistent the american heritage dictionary 5th ed So it appears the standard usage in both side of the atlantic is one unhyphenated word.
Searching sources on google doesn't help much as both variants are widely present there
