Cœurs vaillants : La Grande Guerre

					
German Helmet:

You will be able to pick up a German helmet in Chapter One during the tutorial of the level Casern after blowing up the second target practice dummy with the grenades.
HQ Map:

This item can be found in Chapter One in the Marne Battle level under the bridge. The HQ map is at the foot of the lower ladder behind some reeds, make sure you pick it up before you blow up the bridge.
The Khukuri knife:

You will find the Khukuri Knife in Chapter One in the level Neuve-Chapelle after you help the Indian soldier destroy the floor of the bunker by climbing the ramp and grabbing the collectible on the first floor of the bunker at the base of the first metal ladder.