Re:Natural Casing dogs in San Antonio
San Antonio is not a big hot dog town,its more mexican food and hamburgers.
As far as natural casings go, you could try H.E.B. Grocery Stores.
I don't know about carrying any in your luggage on the plane.
H.E.B. is all over the area.There might be some meat markets, like Penshorn's out in Marion, east of San Antonio, on FM78 or Granzin's off the Interstate 35 North access road in New Braunfels who make their own and sell them.
Or check with H.E.B. Central Market on Broadway, next to the University of the Incarnate Word in Alamo Heights.