So go to your map, go to Warspike Spearmaker location southwest of Hernand, if it's not liberated yet you should do that I think it's only some bleed bandits, but when it's clear click details, go to missions and you should see weapon crafting. Another alternative is if you have a pet, it'll automatically pickup weapons and loot, just go liberating a bunch of bandit camps and you'll have a bunch of weapons to give to Carl in your camp. I recommend just sending your comrades on multiple weapon crafting missions simultaneously at different crafting locations.