You can't. They are just in the special events. They are pretty generic so not really part of the proper tracklist. Thats why the course maker lets you make them too.
You can share user-created circuits online. Use the Eiffel or Tokyo Bay template, create a circuit and share it. Only karts can race on kart tracks, so there's no danger of anyone rocking up in the Ferrari 330 race car.
Is that the case online? I created a Kart track with the Tokyo Bay theme and I had the option of test driving any of my favorited cars on it, which included the Chrome Line Lambo. I might have even taken a normal car around it in Practice mode, I forget. I haven't driven on it online yet though.
The first thing I did when I unlocked the Top Gear Test Track was drive a kartaround it. 1:35 was my best time. I've tried the Nurburgring and found it slihghtly tricky.