there is so little that can go wrong i would think that trying to get the stuff yourself is better. i got lucky and got my b12 off of ebay. i dont think they sell it any more. i already had syringes that i have had forever from some guy in fairbanks, just in case i needed them. they are only half ml so i have to take two shots to get a miligram.
a decent md or nd would hear you out and write a script, out of curiosity if nothing else. you would be hard pressed to hurt yourself with it. nothing different than what a diabetic does all the time.