Extra Flower Cup Tracks are actually Tracks from the first game in the Mario Kart series, Super Mario Kart. The Tracks remain almost the same, with the exception of missing obstacles such as Piranha Plants in Choco Island 1 and Boos in Ghost Valley 2. Some of the backdrops are also different, but the course remains the same.
The Extra Flower Cup Tracks can be unlocked by getting at least a Star rank of one in the Super Circuit Flower Cup. You can access these by pressing L/R on the regular Flower Cup, and then you are able to select the cup.