The Divide has one signature weapon called Red Glare. Red Glare is a missile launcher you can pick up when you are tasked with picking up the laser detonator. Red Glare's upgrades can be randomly found throughout The Divide, but it is very rare. There are a few techniques you can employ in order to get the three upgrades though:
Possess just over 34,000 caps and when ED-E opens up any commissary you can buy they from there. If you plan on using Red Glare the caps are well spent on these upgrades as it makes this weapon much better.
If you do not have 34,000 caps in pure cap form you can sell enough goods in order to afford the upgrades, purchase them, and then just load your previous save to simply avoid having to waste your items/cap collection.
Previously mentioned it is possible to randomly find these upgrades throughout The Divine although it is very rare.
*Note* This can be completed AFTER finishing the main storyline.