Where do they get B12 in B12 shots?

I started working at a hospital as an administrative istant. I want to make the most out of my health care benefits because I I was stuck with crappy, HMO-type health care from previous employers. I am a vegan, and I've been wanting to look into getting a B12 shot at the hospital where I work. Are B12 shots vegan? Do you think they'll give me the shot or will they test me for a B12 deficiency beforehand?