Zauriel,
the Risk 2210 rule book sez you may buy up to 4 command cards per turn.
It’s easy to miss this rule – just a one-liner somewhere near the front of the rule book.
So, that pretty much limits you. You can certainly end up with a pile of cards by turn 5, if you save em… also on each turn you can add a free card (along with a free chip) by virtue taking three territories by combat (doesn’t count if the territory was unoccupied) – but only one such chip-and-card can be earned per turn, regardless of how much turf you overrun.
Also, I can’t recall, but it seems to me that unlike in Risk, in this futuristic update the elimination of an opponent does not yield his cards to your deck. Instead, his cards are eliminated right along with him!
… happy nuking!!