Anmon Guards (The purple, hammer using anmons) apparantly have 100%/99% drop rate, so if you have a 45+, just spam Ellia continent 8-9 times for your jewels.
I suggest using a class good at dungeons though, ST lass, Warlock, Battle Mage, and any Ryan class that can use neph would probably be a good choice.
(favorite classes under title)
Grand Chase (NA)
Dark assasin, Striker, Swordmaster, Dragon Knight, Crossbow(wo)man, Warlord, and Fighter.
Magic Knight (Elsword 2nd job, "magical" branch)