ms contin (morphine) is alot different than oxycodone in my opinion (i'm prescribed both) I find if I take enough morphine to kill pain the pain, i'll be WAYYYYY more fucked up than if I took enough oxycodone to do the same thing.
If you run out you can call your doctor and he can just write you a new script and you can pick it up. A pharmacy isn't allowed to fill a faxed in narcotic prescription though, so you can't just have them send it over.
You can always call up some peoples and buy some pills too, but it would be just as much trouble, and cheaper, to get a new script