I just wanted to post an update. Taking your advice (and knocking the side of my head V-8 style for not thinking of it before), I used actual blood from the meat shop, and set the stains with heat. The resulting stains were good, but not quite dark enough for my tastes (perhaps it was the type of muslin, but the remaining stains were very faint, even without any detergent).
I just happened to have a handful of chokecherries from the little bush/tree I'm nurturing in my back yard, by the way, but on my test cloth, the resulting stain was more wine-colored than I liked.
So I played around with some Rit dyes, and ended up using a combination of liquid "dark brown", a touch of liquid "crimson" and some powdered "golden yellow" dyes, mixed roughly one part dye to twenty parts salted water, and again, let the dye dry naturally, then set the stain with the iron. The result was just what I was looking for - very close to the color of the actual blood, but a little more pronounced, and from the wash test, relatively colorfast.
Anyhow, thank you all for your advice!