Thanks, I added a label to the title to deter people from taking this seriously.
That sounds like too many cards for a single shipping container given the size of a single box
A 40-foot container seems to have an inner volume of 67,5m^3. That's 67500000 cm^3 for 500000 units, making it 135cm^3 per unit, so it looks like you are right.
dang, I messed up the URL, would you mind fixing this?