Use one of the following entries with the giveitem self code. Note: The game appears to have only one type of grenade ammo mod. For example, enter giveitem self 8 X_gammo_incendiary as a code to spawn a level VIII incendiary grenade ammo mod.

X_GAmmo_AntiThorian
X_GAmmo_Cryo
X_GAmmo_Fusion
X_GAmmo_HE
X_GAmmo_Incendiary
X_GAmmo_Proton