If your dry cleaner has already tried then most of the things listed won't have much better results. The blood, itself, is probably long gone but the stain has been set into the fabric. The remaining stain won't do any more harm to the material than the original dye.
I have several pairs of those surplus, OD Green, wool pants (some are 20+ years old). A couple of them have been stained, over the years, and when I see the stain I can, still remember where, how, and when it happened. Not quite as good as field notes or a hunting journal but still a plus.