I buy syringes for my diabetic dog, and use extras for my own IV meth
use, taking care to NEVER mix them up. But you can say the syringes are for your dog, if you'd like to have a story when you go. If asked say your dog receives 5 units of Novolin N every 12 hours and the vet recommended [desired syringes]. Note that dogs require 1/2 inch needles because their skin is thicker than human skin. I get 29 gauge needles and unfortunately due to a particularity of my dog's dose, they're the .3 mL ones so it limits the size of my shots. I would recommend larger volume.
In the US, laws about syringes vary by state. I spent some time in Arizona where a jackass walmart pharmacist refused to sell me needles without veterinary documentation of my dog's diabetes. I had my dog's records in my car but I sought to purchase the needles elsewhere on principle. I told the pharmacist before stalking off that he was not going to stop a single person from injecting illicit drugs
by refusing to sell anyone needles without proof of medical necessity; he was only going to increase the likelihood that some users would inject with another person's needle or an old one that was dirty or blunt enough to cause damage. His response? "I don't have to support the activities of those low-life's."
I shit you not. What an ignorant prick.
But in the Midwest state I currently live in, I just ask for the syringes and that's that. Good luck!