If you want to stop a contraceptive injection, all you need to do is not have your next injection. Your periods and fertility may take a while to return to normal after you stop using the injection. However, it’s possible to get pregnant before your first period after stopping the injection. If you don’t wish to get pregnant then you should use another method of contraception from the day that your injection would’ve been due. If you have sex without using another method of contraception you may want to consider using emergency contraception .
If you're going to use any injectable gear, then of course you're going to need some "darts." You can pick up syringes at your local pharmacy unless your state has certain restrictions. Also, you can purchase needles online. Just do a little searching around and you'll find several places that'll hook you up. Syringes will run you around 50 cents apiece. Note that it'll be more difficult to obtain needles (at least from the larger, more "legit" companies) if you live in California and Illinois. You'll usually need a doctor's prescription in those states. Still, if you look around enough, you can get what you need.