This is quoted from related link on the Thundergun:
The Thundergun is a weapon featured in the zombie mode of Call of Duty: Black Ops, and can be found via an Easter egg in the campaign mission "Numbers".
Read the link for more information on the Thundergun like this trivia "The Thundergun is the only Wonder Weapon so far, when upgraded, that doesn't keep part of it's name"
There is not a glitch for the Thunder Gun
Only in zombies.
from the random box
by going to the random box in zombies
use the ray gun or the thunder gun
You Get your thunder gun from the box if Ur lucky enough u might get it
You can get it in the mystery box in Zombies.
what r the wonder weapons like ray gun n thunder gun in black ops 2 treyarch
the thunder gun and hk21 are the best on black ops
you don't it is random
you get it from the random weapon box by luck.
by using the mystery box and getting lucky