It can't hurt to ask. If anything you can say it's for a friend.
In my experiences, however, I was always offered heroin rather than ever needing to ask around for it. I had a reputation for being a psychotic hardcore drug user, though, so people offered me anything they had if they knew me.
If you're in America, it's fairly uncommon unless you're near or in a large city. It just doesn't make it's way to most suburbs except in really tight circles. Like you said, most people frown upon it, so it's usually kept fairly quiet among a small group of people.
The people you may want to try asking over anyone else, though, would be Oxycontin heads.