It is: /esoui/art/icons/item_generic_coinbag.dds
I don't know of any list with images, yeah that would be nice. But if you find anything you want in the game, in a window or anywhere you can probably use zgoo addon to get it. For example the coin bag icon you asked about appears in loot windows. So you could open a loot window with the icon showing & Put your cursor over it:
Then (with the zgoo addon installed) type /zgoo mouse (which gets information about what your mouse is over) & this window pops up.
Its not always obvious where to look next, you may need to just kind of hunt around in that area for whatever your looking for. But for the icon we need to expand the table by clicking on dataEntry, data, and then again on the next dataEntry to find the icon:
Sometimes its buried a lot deeper & not quite that easy to find, but it gives you a place to start.