How about replacing tabs with newlines first, and then merging 3 lines at a time? In bash, it could be something like this, considering the list is tab separated:
cat "file.txt" | tr "\t" "\n" | while read N1; do read N2; read N3; echo "$N1 $N2 $N3"; done
You may have to modify this to fit your needs.
Of course, there are many other solutions, most of them probably better than this one. It could be done in just about any language.