Hi Mark P.
Your question is a little outside of the scope of the forum since starting a mattress store is a much more complex endeavor than buying a new mattress.
I’m not sure of your level of knowledge and experience in the industry or how familiar you are with mattress components and foam types and quality specs but some of the Texas factory direct and wholesale manufacturers are listed in some of the Texas lists such as the Houston list here, and the Dallas/Ft Worth list here, and the Austin/San Antonio list here that may be worth contacting and may be a place to start.
I don’t know why you are having trouble with getting them to respond to you. I would think that if you call them with more information about you and what your plans are and that you have good plans in place that they would be happy to talk with you.
Phoenix