when i visit family in dallas, i always make a point to hit up central market or a whole foods. good beer is always found there.
goody goody (i know, what a name!!) is a large liquor store chain in TX that has an OK selection and good pricing. should be easy to find these stores.
i doubt there's many of these left, but the tom thumb grocery chain had a higher end store called simon david. the simon david stores used to have a very impressive beer selection. it's been 10 years since i lived in dallas, so i have no idea if these are still around or not.
lastly, if you're further north than dallas itself, in denton... metzler's barbeque has a good selection. from the outside, metzler's will look like a typical convenience store. inside, the place reeks of mesquite smoke and always had a surprisingly good beer selection (bbq wasn't bad either). the first few belgian and german beers i ever had in my life, were all purchased from metzler's in denton. funny thing about that place, due to the mesquite smoking for their barbeque, the beer labels retain that smoke smell. you WILL smell smoke when you handle those bottles!