How would a single person get all of them?
Well, Wild Games bought Decipher's excess storehouses. Maybe the one guy who was in charge of distribution to D'Agents sold them (presumably after he left Decipher...I'm sure that would be a breach of contract...)
Or Decipher could have just said, "Hey, we've got a stack of these in the warehouse. How about $1 per card?
Fiscally, it is not very cost-conscious to print so few versions of a card (a foil, at that) without making it easily and publicly known exactly how few copies are available. What we should really do is see if someone has a list of D'Agents from around that time; I'd suspect they would print two copies of the card per D'Agent and hold onto the surplus. Even if that is 50 copies of the card, that is still much more than 3.
Of course, who knows? There could really just be that one copy and the rest are forgeries.
-wtk
Edit: But if someone wanted to forge a trading card, why wouldn't they pick a game that was more...alive? Like the ridiculously expensive card(S) in Magic: the Gathering?