I've read in a few places that in order to enter Cuba, all foreigners must hold valid travel insurance covering medical expenses before travelling to Cuba.

As an American interested in independent travel (via Cancun), how would I go about getting a policy that doesn't leave a "paper trail" for US government bloodhounds to sniff?

Can I buy it in the Cancun Airport? Is the health policy requirement even enforced? Do they ask for proof upon arrival?