A downloadable version of QUAL_TX without login may be available on the TCEQ website. If not, for any given version, the LA-QUAL model will yield identical results if the the "Model Assumptions" are set to "Texas (TCEQ) defaults" in the menu Preferences/Additional Preferences. LA-QUAL may have newer versions than QUAL-TX with additional enhancements and corrections which will be shown in the version history. Information on LA-QUAL can be found here.
Download zipped file with QUAL-TX executable, license agreement, User's Manual, and example data set (these downloads require login):