You can get most any necessary medication for animals and the requisite equipment for application there. Any vaccine, such as rabies, that has a legal requirement is not sold there, at least as far as domestic pets (cats, dogs) are concerned, nor any medications that require a prescription. We recently got an English Mastiff and did all of his shots save rabies as my wife was able to get everything she needed at Tractor Supply. I would call your local store just to double check but I would bet they have the syringes you need.
They do carry needles and syringes for livestock, not sure about the insulin. They do have some injectable medications locked in cases.
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