There is a page of Armor and Helms, a page of Weapons, but no page for Shields on GFaqs
Shields are listed there among the other items in the Final Fantasy XII: Enemy Drop Guide by wrp103, so it is possible to find the shields that drop from enemies. Most shields have the word "Shield" in them, which makes searching for them considerably easier.
Bear in mind the best shield in the game for most purposes is the Zodiac Escutcheon. The considerably lesser Buckler is also unusually named.
Final Fantasy Wikia, of course, tends not to give a lot of space to lists of any armor or weapons from a specific game, but rather records which items are recurring ones. The Shields article does put them all in one list, with stats.
The Armor Images category on FF Wiki has a decent collection of pics of shields, many of them not used in articles, including the one above of the Ensanguined Shield
Should anyone wish to make a full list of shields, with the sources shown, it would save having to go between the GameFaqs and FF Wikia lists to find shields that can only be found in treasure chests without having to go through the series of links, or switch from one GF guide to another