Plenty of the songs I went hunting for weren't available through the standardsearch bar, but, not surprisingly, were numerous when looking through YouTube's collections -- of course, as ever with YouTube, there's the standard quality disclaimer here: there's a decent chance you're not getting the same studio quality tracks you're going to see on a Spotify.
Newly discovered code in a Google page hints that it might just become part of the standard web search interface -- provided you opt to turn it on, of course.