Where do we find it ?

Thanx all.

There isn't one, so unless you equip them with specific weapons and use those values instead, their default attacks will only cause a crit if one of their special actions has a success or boon line that causes a crit.

Or they get a Comet when attacking with an Expertise die.

Is that a simple omission on the part of the designers ? Should they have a CR ? Or is it designed as such ?

A Choppa with no CR... Seems strange...

Where its obvious the NPC is using some kind of weapon, I'm going to base the CR on the weapon used (which i will determine using the base damage as listed in the NPC description)

where the NPC isn't neccessarily using a weapon but instead fights unarmed, I'm going to give them a CR on the fly by comparing their unarmed damage to base "human" unarmed damage, and working out a corresponing CR that seems appropriate to me...

Let's consider for a moment that a PC with a Hand Weapon has a DR of 5 and a CR of 3. When they make a Melee Strike, they can do normal damage with a success or +2 damage with three successes. In addition, if they get 3 boons they can trigger a crit due to CR.

An Orc has a default DR of 5 (same as a hand weapon) and no CR, but has a special action called Chop! which, like a basic action, has no recharge and can be attempted every turn. Sure it has an extra misfortune die modifier, but this can be ignored if they outnumber their opponents. This is very much in keeping with the the fluff of greenskins morale. The effect says the creature strikes with its weapon at the enemy, but does not specify what that weapon is. Like Melee Strike, the attack inflicts normal damage with a single success. With 3 successes, the attack does +1 damage and inflicts a fatigue rather than doing +2 damage. Since characters have to worry far more about passing out from fatigue than from exceeding their wound threshold, this is arguably a better result since it's easier to put a PC down for the count. Also, the Orc will trigger a crit with two boons using this action vs. the 3 needed by a hand weapon used to make a melee strike.

So I contend that the special action Chop! already represents the creature's default weapon, a Choppa in the case of Orcs, because their "standard" melee attack is more likely to cause a crit than a melee strike with a hand weapon. Also remember that the system is designed so that most of the time you are just using the default entries for creatures, which keeps things simple and easy for the GM, rather than having to reference individual weapon stats all the time. If you create a separate weapon entry for Choppa and then just always have your Orcs armed with them, you in effect have replaced the default. I would be very wary of house ruling a separate weapon entry for Choppa that was better than a hand weapon since when combined with Chop! it may make Orcs more powerful than intended. Far easier to assume that Chop! is available to Orcs because they are armed with Choppas.