Keep doing Felix leads, until you get a large supplier mission. Go to that supplier and negotiate for the coke. Once you have it, start the smuggler mission (it is right where you buy the coke). The smuggle mission is where you drive your coke back to the storehouse (you need to have obtained at least one storehouse to start getting money from your fronts). Once the coke is safely in your storehouse.....you will now have a "distribute" option as one of your missions. On the distribute missions, you not only supply your fronts with large amounts of coke, but you also pick up your money at the same time.