I live in Texas also and will ignore their intrusions into my rights.
If the federal government outlawed the selling of multiple round magazines, they wouldn't be sold in this country so you couldn't get one even if you lived in Texas - there wouldn't be any sold any more. Maybe, or not, you could find one a private person had and purchase that but that would be the only way to get one.
As laws have already been passed, if you look on websites of companies that sell these multiple round magazines, you will see they list the states and cities where they can't sell you a magazine, so you can't order one if you live in those restricted states/cities.