Authentic Mexican food is not hard to find in Las Vegas. Just don't expect to get it anywhere near the strip. Good Mexican on the strip? Yes. Authentic? No, senor.
So go, rent a car for a day and venture off the beaten path as if you would if you were to visit Paris or London. You are not just going to the Louvre or Buckingham Palace for changing of the guards. You would look for that Bistro which serves excellent boeuf bourguignon, or that really tasty Black Pudding in a Pub in London....why do most people only venture off the strip to go to an outlet mall?
These people did it and found a great spot even I was not aware of while living in Vegas:
Personally I ventured back to North Las Vegas to satisfy my craving for Tacos. You may remember this post:
A bit further east, past La Bonita, I saw this shanty style set up and the sign for .59 tacos (which I did not order). Made me stop. Hungry, tired of looking for even more authentic fare, I stopped in and had my fill. Authentic it was. Heck, even the Coca Cola was imported from Mexico. That's first. I asked about the difference and got a shrug. It may be that this one was made with sugar and here they use corn syrup? Not sure.
I ordered a Gordita, which basically is a fat Taco. Thicker and more stuffing....I was hungry. Served with rice and beans, they also offered a Taco al Pastor, maybe they saw the tourist in me? All gluten free by the way and the check came in at 8.75.
Do I have to tell you more food stories for you to venture off strip? I got a couple more. Pizza and coffee. Suburbs.