Sounds like BS, frankly. Or someone who doesn't know what they're talking about. At a minimum, they're confusing/oversimplifying the truth.
If your doc doesn't want to prescribe you the 5/500 Roxicet/Percocet with APAP/Acetaminophen (or the 5/325, or Oxycodone with Ibuprofen, etc) and wants only the oxycodone alone, there are various forms of it. I suspect that at most, the supplier your pharmacy usually gets the prescribed form is no longer available in your area.
I'm sure that your doc can write out a new script for a form that the pharmacy can fill. Call your doc, tell him/her which pharmacy you go to, and have him/her ask them what they have in stock that they can fill right now. It may not even be oxycodone at all -- it might only be Hydrocodone (make sure that he knows they aren't equivalent if so; 5mg oxy is roughly equal to 7.5mg hydro for most people, for some the conversion is closer to 5->10), but at least it will keep you out of withdrawal and your pain somewhat under control until you can settle on a long-term solution.
If your doc accidentally wrote the script differently (say "oxycodone IR 5mg" versus having previously written just "oxycodone 5mg") then simply re-writing to the previous phrasing may solve your problem. Pharmacists can be highly variable in terms of how they'll interpret the phrasing of prescriptions. Some will honor the obvious intent of the script, others will strictly stick to the letter of what's written even when the intended medication is clear and available. Particularly when it comes to opiates and other "abusable" meds.
Conditions: Reactive Arthritis (AKA Reiter Syndrome), Crohn's Disease, Chronic Pelvic Inflammatory Syndrome, Sacroiliitis, Costochondritis, As Yet Unknown MS-Like Relapsing/Remitting Neuropathy, and a partridge in a pear tree.
Medications: Currently not that many are taken daily, but there are many at my disposal for part-time use. Low dose pain medication, after years at high doses. Working on innovative ways of taking lesser-known pharmaceuticals and non-prescription supplements to maximum benefit.