Hi Salsalisa, i’ve recently started making tortillas at home too, after purchase of a press. we buy masa harina at the grocery store, but you can order it online. Just google “masa harina amazon” and a bunch should come up, and in manageable-sized portions.
the one i’ve been using does not give me the results i’m looking for, however - the Maseca brand. it doesn’t taste corny enough to me. You also need to be careful with the press as it makes them really thin if you press them all the way, and my favorite kind are the thicker ones.
i’m going to try ordering a different type of masa harina online myself and see if my results vary. one tip i was given by a server at a mexican restaurant regarding more flavor - she said that i probably needed to add more salt.
but really, i think a lot of restaurants that make really good tortillas get their bulk masa made by someone who is actually grinding their own corn. something i’m not prepared to do… good luck!