Can't seem to find the Zilla Shotgun for whatever reason?

[floobadoo]

I have been very close to 100%ing the ammonomicon for a while, the only two remaining things being the Zilla Shotgun and Rubenstein's monster. Rubenstein's monster makes sense as one that might take a while to get since it requires getting both Rube guns in one run, but I am more wierded out by not being able to find the Zilla Shotgun. According to the enter the Gungeon wiki the Zilla Shotgun is unlocked by default. I am just double checking here to make sure there are no reasons these things aren't showing up besides RNG?

[Black Heretic]

No restrictions or conditions to satisfy for it, as far as I know. I suggest you to play with rainbow chests enabled, it should be easier for you to find it this way.
If it can make you feel better, I only miss Ballistic Boots and Rubenstein's Monster, and the former cannot even drop from a rainbow chest.