You can download free mp3 files of hundreds of commercially available tracks from this site. Each track starts with a short advert and the “artwork” that appears in iTunes is linked to the advert and not the album.
It’s dead easy to edit off the advert using Audacity, Amadeus Pro or other audio editing software that will save mp3 files. The art work can be replaced in iTunes too by grabbing the thumbnail from Amazon.
The sample rate is 192kbps so they’re good quality too. So if you want a tune check this site first before buying it from anywhere else.