Equipment stores are located on most of the planets or bases you may come across. You can purchase and sell Armor, Rifles, Pistols, Munitions, etc at Equipment Stores. Generally you sell items at only half the original purchase price, even less if they are damaged (armor) or partly used up (ammo, pepper spray).
The gun and rifle weights and prices below refer to an empty weapon without magazines in them, those for ammo and pepper spray are for a full item. The Kilrathi weapon/ammo, Brilliance and Ultimate purchase prices are theoretical, as they cannot be bought, only sold (for half the price).