Breath of Fire IV - Nina's Best Equipment

 Ouroboros - 96 attack.  Casts Raise Dead if used as an item.  Steal from Beihl in the basement of the Imperial Castle.
 
Angel's Vest - 94 defence.  Steal from a Warder in the Imperial Castle.

OR

Star Dress - 92 defence.  Manillo Store in Astana near the end of the game.  Whale x 3, Acheron x 8.

You'll find both Warder and Beihl in the basement of the Imperial Castle.  It shouldn't take more than 20 or so steals to get the desired items.  Star Dress isn't really worth it, since Angel's Vest is so easy to get.  Unless you want to get eight Acherons, in which case, what else are you going to spend them on?

I found Warders appeared most often on B1.