There were a number of militia acts passed by the Congress of Texas and the Texas Legislature. The state was divided up into a number of militia districts. For the basic source I would browse through Gammel's Laws of Texas at http://texinfo.library.unt.edu/lawsoftexas/default.htm
It is a PDF format and tends to freeze up on my computer, but if you want the organizational structure, I would start there. There are some files on the various districts at the Texas State Archives. However, many did not survive the 1880 Capitol fire, so they are by no means complete. Occasionally you can find some references in county commissioners' court minutes, but that too is hit and miss.

In terms of civil war period acts, one was passed February 14, 1860, a second on December 25, 1861, and a third on March 7, 1863. I do not have dates on the earlier ones, you will have to browse Gammels. A significant conflict arose between Texas and the CS authorities, as militia could not be compelled to serve outside the state. There was near rebellion in the German areas below Austin in early 1863 over this issue.

I am not aware of anyone who has done a serious study of this subject. HAve fun.