In reply to Timmd:
If the house is already on the market then the seller is likely to be in a contract that means they are bound to pay a commission or fee to their agent regardless of whether it is the agent that makes the introduction.
If your friend is not looking at houses that are already on the market then you have a few options. You can leaflet drop your favoured area, put up a card in local post office/shop etc or you could try a post on the local facebook pages.
I tried the card in the local shop about 20 years ago and didn't get much from it. Putting post on a local Facebook page recently got the inevitable replies with people linking me to stuff on the open market but I did also get a few private messages. Worth noting that my original post made it very clear that I was not business and that any contact would be treated with strictest confidence.
Good luck.