[kbr2000]

I came up with:

  gawk 'BEGIN {IGNORECASE=1} ((length($1) == 6) && /^[a-fois]+$/) {gsub(/o/,0);gsub(/i/,1);gsub(/s/,5); print toupper("#"$1)}' /usr/share/dict/words

(caveat: it does not filter out duplicates)