Tourism information offices and desks in Amalfi Coast
It helps to know this: Although the main gateway to the Amalfi Coast (for most visitors) is Sorrento, which lies in the Province of Naples, the Amalfi Coast itself lies in the Provincia di Salerno province—therefore, in über-bureaucratic Italy, the provincial office of Salerno and its satellites are where you will find the official information about most of the Amalfi Coast.
Unfortunately, the proper way to do the Amalfi Coast actually ends in Salerno, so chances are you will not have a chance to visit its tourist office first (assuming you go to Salerno at all; most do not bother—and, frankly, aren't missing much).
Good thing so much info is available online these days—and the Salerno Tourism website (Turismoinsalerno.it) is almost unique in Italy for also freely including plenty of information about its neighboring provinces as well. So, for example, its interactive clickable maps also give you intel on, say, the Monti Lattari Park, which forms the spine of the Sorrentine Peninsula above the Amalfi Coast but, technically, lies largely in Naples' province. Nice.
That said, the Sorrento tourism office does have good general information on the region (as well as a killer cafe terrace for sunset drinks), and most of the larger towns have their own tiny visitor information offices as well.