Yea... Oxycodone is generally one of those drugs that you won't find on the streets here in Australia, due to it's rarity and stringent control. It is treasured among drug users, even those that aren't too fond of Heroin, for obvious reasons. It's a fairly unique opioid too. Tends to release a somewhat stimulant-like buzz, yet also (in the higher dose range) has the potential to make one nod. Most people that have a script for Oxycodone probably aren't too fond of the idea of parting with such a useful pain-killer either, unless they sell their Oxys and buy illicit Heroin for better pain-relief and euphoria.
I guess it's the case with benzos too. Alot of people that are prescribed anxyolitics like clonazepam and Alprazolam wouldn't be overly enthusiastic parting with their meds, because of how hard it is to get a steady on-going script of them and due to the fact that they would legitimately need them to relieve them of anxiety, or sleeping-disorders.
Having said all that though, I think if there were to be a sudden influx of prescription opioids and benzos hit the streets, they'd either (a) be imported from International pharmacies, or (b) someone that works or has access in the pharmaceutical industry has been getting "itchy-fingers" and selling them on the street.
I have a friend who used to be a Heroin dealer in C.B.D. that just recently told me that back in the day (when they were on the market) there was a pill addicts used to call "footies/footballs", that were widely sought-after, because they contained a liquid form (20mg's) of Temazepam, which means that it was injectable and they were actually more expensive than a cap of Heroin.