If you're not doing it for profit, you could probably* do what I'm doing for a project I've been working on, and just use whatever art you find online. Pinterest and Deviantart are great sources for all kinds of pictures/artwork. Just Google whatever it is you want, then click the "Images" tab at the top, and away you go. You'll most likely have to click the pictures and go to whatever site they're on in order to get something with good size/quality, but that's what Right Click, "Open in New Tab" is for.
* I'm not making something for sale, or most likely even for public consumption, just for my gaming group.