The qualification I'd make to what Harvey wrote is that, where a recording is no longer available in its original form - especially when that is because the publisher doesn't see it as commercially viable - it ought to be possible to download it via the net.

I'd like to see some online source of these, geared towards folk music - with some way of using this to channel money to the musicians involved.

Generally speaking I prefer to buy recordings direct, from the side of the stage or whatever, knowing that all the money goes to the artiste; or from record sellers at festivals, who are part of the folk world, employing musicians as staff and that kind of thing. (And from jumble sales, boot fairs, charity shops and such, which are the only place to find lots of recordings – though in principle there's not much difference between buying a record second-hand and copying it. In neither case does the artiste get any additional payment on top of the original record sale. But it's a matter of scale, which is what really matters.)