Many items in Atrinik are 2D, like weapons, coins, scrolls, etc. We use many images from http://www.molotov.nu/Graphics/Angband/Inventory/
(which can be found from one of the links above).
Also not all of the above are free/GPL (some have own licenses, some are unclear, etc, so please be careful).
Another source we use is RLTiles: http://rltiles.sourceforge.net/
"zerosumtiles" is another source, but I forgot where that came from and its license (but I think it was public domain); you can find it attached.