I know this is one old thread but since i have finished ffXII recently i was browsing this forum. Personally i have very few of the rare items mentioned and I know there are a lot of them just by looking at the licence board.
Anyway, speaking or rare items i have only managed to get ribbon (which is an extremely helpful accesory), the ensanguined shield and the ring of renewal (another good accesory that boosts defence). I got all of them in the hidden area in Henne Mines (the one which leads to zodiark) by reentering the area 3 or 4 times. This random respawing treasure system the game uses gave me each time from very useless to very usefull items.

Now I am exploring the upper part of Great Crustal but so far i managed to get only i maximilian armour. Does anyone know how can i get the diamond armlet (which according to your posts raises the likelihood of rare items to appear) ?