SPOILERS
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There are plenty of ways to get your AC down without cheating.
Robe of Vecna - available if you have the bonus CD - you can download the merchants which sell extra goods in a very small zip file (1kb) - you can find the download Bonus CD here:
http://www.sorcerers.net/Games/BG2/index_editors.htm
This is not cheating - it is a legitimate BGII add on which was a special CD for people who pre-ordered the game. The robe lowers your base AC to 5.
Robe of the Good Archmagi - if your character is good this can be bought in Trademeet - there are also Neutral or Evil ones, but I don't know where.
As others have said the Bracers AC3 are great.
Elven chain mail can be used by mages & they can cast while wearing it, but it is not available until late in the game. It's also a stylish metallic green colour as a bonus. Drow elven chain works the same, but can only be used in the underdark.
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Time is an illusion. Lunchtime doubly so.
Epona of The Laughing Hyenas and The Ladies Guild.