Go to any pharmacy and ask for the kind you like to use, they cannot tell you no. You could even tell them it's for IV drug use (not smart IMO) and they still have to sell them to you. I have been to a few places that try and say I need a Rx and I called their BS and got my rigs.
Just make sure you know what you are talking about when requesting them, or you may end up getting the run around. And if they think they can fool you they will try and not sell them to you. I have had this happen only because I had asked for a 10pack and not an entire box, they kinda gave me a hard time but I got them.
Unless you are looking for a needle exchange, just go to a pharmacy.
-Noddy