I use b-12 frequently.
There are many sites that sell it but the way I got mine was to go with a friend who raises farm animals.
He was getting some other medicines for his animals and I just put a 100ml bottle on the counter with no problem.
It was 8 dollars if I re-call and all the online places charge a lot more.So if you know a farmer it's easy to get.
Cynocobolamin is the same whether it's for animals or people. It's used for sheep, cattle, hogs, chickens, cats, dogs, etc.
From what I have read many endurance athlets use it and as was mentioned above oxidizes the blood.
I give myself a shot 1ml when ever I feel the need.