A vial is a container, not a measurement
RAW you need the container, not just the blood. The spell says “vial of blood” - it means both the vial and the blood.
However, since the “vial of blood from a humanoid killed within the past 24 hours” has no cost, RAW, there is always one in your Component Pouch. How does it get there? RAW doesn’t say.
Equally, RAW, it can be replaced with a focus.