Corn tortillas from masa harina are not very good. I would avoid them
altogether. To get the best possible corn tortillas, you should either buy
fresh masa from a local tortilla factory or mexican grocery (no more than
one or two days old) or make it yourself. If you have a burr mill, it's
very easy to make.
Boil corn in slaked lime for a bit, let rest, wash, grind, press, and
grill. See
http://gourmetsleuth.com/masanixtamal.htm
for excellent details. You can buy corn from them, but most mexican
groceries have corn for pozole at something like $1/lb. I use a kitchenaid
grain mill to grind my nixtamal, but a corona mill is supposed to be better
at damp grinding.
raj