http://opengameart.org/content/more-rpg-enemies
These fit our style really well, and include a gargoyle (which is one of the few enemies mentioned in the narrative). The only issue is that they are smaller than I would like. Scaling them up by 4x makes them larger than I would like. Might try seeing how well they look if I scale it somewhere inbetween, or might just use them directly and not be too picky about it. These don't, however, cover sprites on the map. I suppose it wouldn't be too much work to make simplified versions of them for use on the map.

That only leaves the armored beast sprite (the second boss in the prologue chapter). We might find something suitable and substitute that for the beast. Ideally though, I'd like to create our own sprite for this. I'm not going to be picky about it though.