Methylcobalamin (Methyl B12) for cats is widely available through pet-specific retailers, major online marketplaces, and some human-grade sources, provided they are free of harmful additives like Xylitol. It is most commonly used to support cats with diabetic neuropathy or kidney issues. Where to Buy Methyl B12 for Cats Methyl B-12 Supplement (4 fl oz) - PetTest Connect With Us. (888) 469-3579. Liquid Vitamin B-12 for Dogs and Cats - eBay