Finding Grenade launcher ammo for getting a relic on Research base

I have completed the game already and i am at 99% completion right now I need to find just one relic on the Research Base which requires the use of a grenade launcher to blow up the wall to get it, unfortunately since i have beat the game and killed all the enemies I couldn't find any ammo of the grenade launcher and i circled the entire Shipwreck beach, Hillside bunker and research base to find any but still unable to do it,Given the fact that grenade launcher comes only in the later levels it doesn't make sense for me to look at the older levels like Shanky town and mountain temple. Has anyone else run into this issue and found the ammo needed? It's very annoying because getting all the documents is worth 50G Gamer points and also will pave the way to getting salvages for the updates to my last weapon(rest of them all are upgraded) which is another 50G.

Map location would be greatly helpful because even with the Fast Travel there is still lots of spaces you have to cover by running still.

My cousin encountered this, and I believe what he did was port to Shantytown (since enemies respawn there most of the time) killed enemies and just looted them. Then just repeat the process until you get one from an enemy. If you want you can try your chances at the Hillside Bunker or Research Lab after trying this.

Be sure to use your rifle to kill them, it would be better if you have the Scavenging skill from the Survival tree to increase your chances.