Mario Kart Wii Platinum Soundtrack was released in 2011 as a platinum reward exclusively for the now discontinued Club Nintendo. It's one disc and contains 43 tracks. The soundtrack is composed by Asuka Ohta & Ryo Nagamatsu. I noticed that some of the track information was different on my CD than I've seen on other rips online. So, I did some digging and found out that the titles vary depending on the N.A. Version, European Version and the direct Japanese translation. I ultimately chose the titles that sound the most natural out of the three—in case you're wondering why the track titles differ slightly. See the tracklist on VGMdb to see what I mean.
You can still find copies floating around ebay ranging from about $60 - $80. In case you had some extra cash and wanted the physical copy but if not, you'll find Mario Kart Wii Platinum Soundtrack in our archives.