Join a hunt LS immediately. Naul spawns every 30-45 minutes give or take so just keep an eye out in the Hunt LS' that you are a part of and linger around Coerthas.
I assure you. Once you join a Link Shell (or two) that is dedicated to hunting marks, you just join a party, do your own thing, and when they are called out you warp and kill them.
I have like 500 some odd seals just from about 6 hours of on and off hunting because of the spawn rates and the amount of B and A ranks that I down. A lot of people in my parties have also received the Bloody Logs (poor translation I think

) from some of the hunts too and have already (in two days) BOUGHT their weathered weapon AND used a sand of time on it.
This business is easy with the right groups.