It's Cyberspace

Even before the 3rd Lap (when the super item box spawns), there are enough item boxes littered throughout the course.
There is one on each branching path at the start of the track.



One before you go into the plane section.


In said plane section, there are 2 sets of 2 item boxes that circle the Spike Ball X's.


Lastly, there is one just before the highway section with the trucks.


I'll also mention the Super Item, which spawns halfway through the plane section near the bottom of the 2 roads.


Assuming you grab 4 on the first lap and grab the 2nd one at the beginning (on the path you didn't take) on the 2nd lap, the achievement should be easily got.

If you grab an item box in the Spike ball X's in the plane section, the ones you didn't grab in the X's seem to despawn for the rest of the time trial.

This is probably intentional, but doesn't really matter in regard to the achievement in question. Thought I should mention it anyway.

If this guide helped you somehow or you wanna get some good karma points, feel free to give me your money steam points and drop an award or 10 on the guide.