Also saw Wishes and Hallowishes but didn't get them this trip so not sure how much they were. Illuminations: this one was I think $18 and I didn't buy it so not sure what all is on it. All of these CDs are available at the World of Disney Store at Downtown Disney, but when you call WDW Mail Order, they'll have a master list and can usually find things even if you don't know what store they were in.many of them are available at a lot of stores around the parks. Here's more info on the ones I know about.
You can order from Walt Disney Mail Order as well at 40 or e-mail (although several people have said it is much faster just to call them even if it is long distance for you. It's $14.99 right now (since it is from 2005) Go to Amazon and search for Disney's Happiest Celebration on Earth. Type 'Disney' into the search box on iTunes Store, but there aren't any real park music ones like you are talking about.