Aye. I've been using two things for my graphics 'source'.
The War3 undead strategy guide:
http://www.battle.net/war3/undead/
And from a in-game screenshot taken at 1280x1024
Like Bohorroth, I've manipulated the graphics quite heavily. So you won't necissarily find 'exact peices anywhere. You could make a gui directly from some of these sources ( like any of the War3 race UIs. ) But I chose to mix it up a little.