There are a total of 68 game cards you have to collect for this achievement. They have to be gained through different game modes and are dispersed thusly:
20 Cards from Challenge Mode. (1 from each platinum medal earned)
12 Cards from Time Trial Mode. (1 from each time trial beaten)
24 Cards from winning both races in Race Weekend Mode. (2 per track)
12 Cards from winning Championship Mode with each team. (1 from each team)
If you are struggling with this achievement then look at other achievement solutions for tips.