I have to agree with James, as I am not a legal rep. You may be able to get the information you need from the Texas Workforce Commission, but a CPA is a solid paid option.
I have done freelance work from Texas for a company out of state. It was a nightmare for a number of reasons, but filing taxes was fairly straight forward. I did have to look into some of the legal aspects to cover my own ass after things went south.
Basically, from what it boiled down to when I was looking into it, as a person doing work for themselves in Texas, filing in Texas, they just need a 1099-misc. The concept and responsibility of the work being in another state is actually shifted to the contracting company, who is required to state that they are hiring people in Texas and file with the workforce.
The TL;DR version is I didn't file one because the work was considered to be done in Texas, not another state. This may not apply in your situation; also this was quite a few years ago now and the information was gathered after needing it, so definitely double check and consult with a pro.