Where are you located? Depending on this, you can get needles from either a needle exchange, a pharmacy in your area, or by ordering online. Since I don't know where you are I don't know which of those are your best option. Some states have needle exchanges which are a great option as they are free and carry other HR supplies and can help you with any questions you may have. Some states allow you to go to the pharmacy and buy any amount of rigs, some allow you to buy 10 or less only. Online is a bit trickier since if your state does not allow you to purchase rigs without a prescription, then this doesn't change just by ordering online. You also need to be able to get micron filters.
That being said, if you don't know whether or not you can inject oxy, you don't need to try it. It sounds like you may not be an iv user already, and if that is the case please don't start. Especially not with something like oxy that has such a high oral BA. Have you tried rectal administration? It has all the perks of iv without the risks.
It sounds like you need to do some reading before persuing this any further. Bluelight has a lot of great links, I reccomend the iv complications megathreads, the case study thread, and the plugging megathread. Please don't attempt to iv before you have done your research, tried other ROA, and really considered if it will be a positive step forward in your life (HINT: it fucking won't).
Oh and there's no way to flush oxy from your system dude.