By THÉRÈSE MARGOLIS     There’s no dish more Spanish than ham – the country’s legendary fatty cured pork – and no ham more delicious than jamón ibérico, produced from the acorn-grazed, black-hoofed Iberian pigs found only in the mountainous southern and southwestern regions of that European nation. But while most Mexicans are more than willing to savor the wonderfully air-cured pork