Beekeeping is a legitimate Agricultural item according to the State of Texas (and there is no minimum number of hives required) - which means you can get a number from the state which will allow you to purchase beekeeping supplies free from sales taxes. There are 2 parts to being able to purchase your beekeeping supplies:

1. You have to get an "Ag/Timber Registration number". The easiest way to do this is to go to http://comptroller.texas.gov/taxinfo/agriculture/ and apply online.
2. Once you get your number, you will need to give every store a copy of the "Sales Tax Exempt Form". The link is a form fillable .pdf form from the state comptrollers office you can download to your computer so you can print (or email) as many copies of it as you need.