You say there are friends you could try? In your shoes I would start trying to track down the father. Try things like Facebook, old friends, searches on his name (depending what he does you might be surprised), attempts to find his family (if they might be easier to reach) and so on. I used to be an investigative journalist, and this isn't as improbable as it sounds.
DO NOT tell DS you are doing this, but follow up any avenues you have.
The world has changed so much, even in the last 8 years (since you were pg) that Oz is not so far away, nor people so hard to find, as they were.
When you get in touch with him, tell him that his son has finally reached an age where he really wants to know about his father, and ask him how he feels about that.
In the intervening years he may have come to regret never meeting his child. He may have grown up, started another family, got a well-paid job - who knows?
If Ex is prepared to get in touch with his son you could arrange for them to Skype each other, perhaps?
If he's not interested, you aren't any further back than you were. And that's why you can't tell DS till you have an answer - in case the answer is no.
He's that boy's only father, and it's worth your time to try to find him now DS wants to know. If it doesn't work, or he says no, then in a few more years, when DS is a big teenager, you can tell him you tried, if you judge it's the right thing to do. After all these years I'm assuming it can't really hurt you anymore, and anyway, certainly not enough to justify not trying.
If you decide to try, and you want a hand, I'd be happy to help with suggestions, or actually searching. I managed to track down friends I'd lost for years with a bit of hard work. It can be done.