When you are specific like above, YOU should be doing the leg work to find the image that you want imbeded into your sig. Most of the time I spend making sigs for people is balancing colors and layers, I don't want to spend a few hours looking for the image of "an evil guy holding a sword with blood dripping off of it" because that's a tough search. Go to Google, type in what you're looking for and hit Images... you'll see a bunch of images. It's a start.
I've almost stopped doing sigs all together because:
A: People rotate through them to a new one every week.
B: People aren't specific enough and don't like what's made.
C: People are too specific but aren't willing to do any leg work for the images.
I know it's easy to just request something, but if you want it bad enough... do some work. I do see some people post images saying they'd like it worked into a sig. That is appreciated more than you'll ever know.