When I did mine a month ago, I was hanging out in the middle area of Map 3 of Castle Zvahl Baileys - Map 3
It's basically in the area where the NM Demons are at, but one step down, which will let you land in 4 different paths (you'll know when you see it). From there, there's 2 eyes in each path, 1-2 eyes going through the corridor.
There's one huge hole in the center that leads to map 4 (so careful not to walk over it), so you'll need to bring along a range attack weapon or equip Cannonball or Pinecone Bomb to pull all the eye to you from different paths (9-10 Eyes). Since they all link, I recommend equipping Yawn and/or Pinecone Bomb to sleep adds, which will be necessary to kill at a reasonable rate solo. I also highly recommend buying an Imperial Egg
for Pinecone Bomb
You should be able to kill 25+ Eyes in a single Darksday, or 35-40+ if you have a party set up to cover each path. Since you'll be killing so fast, you can backtrack a bit and nab an extra Eye going back to camp.
If you have a mule in Sandy, there's a weather NPC in S.Sandy. Gloomy weather is common, so you might be able to clear your sword in 2-3 days if you watch for it. Otherwise, if you have a full time job like me, a week.
And to clear things up, since I do get this questioned a lot, physical BLU spells follow the same acc. formula as regular melee attacks. Often times without food bonuses, you won't be able to cap your physical spell acc. on tough mobs like Mamools. Even with food like Pizza or Sole Sushi, you still won't cap on some mobs due to slots being occupied for Blue magic Skill, STR, DEX, etc. If you can find a balance with M.Accuracy equipment, you'll notice your stun durations will be longer and they will proc on things that are unusually harder to stun (Hydra in Dynamis Tav). Not just Head Butts, but things like Sub-Zero Smash, Pinecone Bomb, Sprout Smack and such. Sometimes, you'll need to equip M.Acc over max damage for the procs, which some BLUs neglect.