Well, answering your actual question, I don't have much idea where to get stuff like map icons. I've searched high and low for them too. Any bitmap you find though if fine, but I get the feeling you're looking more for vector-type images, which scale nicer.
Try NBOS online, you can pick up (very) few symbols there. The rest you're going to have to make yourself. Stick 'em in a dirctory in your MapArt directory and go from there.
If you find a source of these symbols, please share em.