Combat Master gives you +1 attack AND makes you immune to all-alone.
But as far as the original question, no. There are, however, some cases where a monster from a random happening or scenario will always have 1 attack per model it is in base to base with, but that is a rule that is not in ANY playable warbands.
EDIT: The combat master skill, iirc, gives only one extra attack...not one per model. Sorry if I worded that wrong.