Was looking back over the rules and as with the 4th edition book you can buy an additional klaw arm which in the old book mentioned with each additional arm the model gained an attack.
Dreadnoughts get extra attacks for every weapon past the second one, check out the BRB instead of the Codex.
BRB Under Walkers and Assaults
Bonus attack for every melee weapon past the first, so 2 weapons for +1 attack (as per almost everything else) and 3 weapons for +2 attacks. Obviously if a weapon arm is destroyed it drops down again, and naturally they lose the use of the profile for the destroyed weapon. (yay for my dreadnought bonking noggins with his assault cannon, a situation I find myself in faaar too often).
I'm assuming Ntaw meant extra EXTRA attacks, i.e. on top of the attacks that everything else dual wielding bananas (or a banana and water pistol) get anyway.
Fun fact: Immobilised / Stunned walkers (NOT Shaken (stirred)) fight in close combat with 1 less attack than normal, to a minimum of 1, and can't sweep / pile in / consolidate.
Hoping this really was the question, otherwise yay for tangents!