for spirits who have an unarmed attack of Force - # ...say a Fire Elemental with an attack of 'Force - 2 M'...

what if their force is a 2 or 1? do you allow the damage to be 0M and just say that they can't attack, or is it like attributes where there is always at least 1?

sorry, but i couldn't find anything in SR3 about this...

Yes, certain spirits are gimps at low force when fighting, but the minimum power would be 1 after all modifications.

Remember that a fire elemental can turn its flame aura on to grant a +2 power on physical attacks.

In your case, the person being attacked still needs to roll against a TN of 2 to stage down. 3-4 F1 fire elementals will still ruin a runner's day.