Most animal produce is only a good source of B12 because the animals have been supplemented themselves. Lack of B12 is more an effect of industrialization of the food production. Less of the type of diet you choose.
Here in the UK a single 250ml 'energy drink' gives you 80% of the RDA for B12 (depending on brand), though as with lots of RDA's when you start really digging in you find a lot of them are old and possibly dated.