All I can add is that I have used goldpharma.com in the past (years ago) to buy injectable B12. I have not tried since they made it harder to be able to do so in the UK.
Used to be fine EU to UK because of some loop hole, gone now.
I am actually on my last vile of methylcobalamin. I was able to get a pack from b12d.org charity before they were stopped from doing it.
Came in 5mg viles that I needed to separate into like five syringes, but I did ten. I have nine left of the syringes in the fridge and then thats it.
The vile was even out of date by over 18 months, so probably broken down to hydroxo by now but its in saline I believe. Should be fine, its all I have but hopefully will not need ever again now.
Daniel