I assume you mean a list of values that you can use in the "ItemTypeIcon" property of an item or block?
If so - there is a list of .tga icons, which can be used with buffs, in XML.txt (starting on line 1793). However, not all of them can be used for the value of "ItemTypeIcon". You need the ones that start with "ui_game_symbol". That prefix is added in controls.xml and windows.xml, so don't include the prefix in the "ItemTypeIcon" value.
But, long as that list is, it isn't complete. So, you could also search the code for other "ItemTypeIcon" values that TFP use, and include them.
Short of decompiling the Unity bundles, I think that's as much information as you're going to get.