As a Contributing Member, you have the ability to post in
the classifieds section which is the proper place to post a Want To Buy ad.
That said, it's incredibly rare to come across a failing or faulty S+ power supply, even this many years after the machine was built. There is more than likely a short somewhere (a typical issue is that the machine was transported with coins in the hopper, and coins spilled out and are under the motherboard or inside the power supply enclosure, causing a short circuit).
While your friend can certainly throw parts at the machine in the hopes of fixing it, it's likely that he's just going to waste money buying a new power supply just to find out that there's nothing wrong with the one he has.