TA stands for total alkalinity and you should have a TA test in your kit, assuming you have the Taylor 2006 which is our recommended testkit.

You can buy MA, muriatic acid, in the paint section of any hardware or big box home store. Here is a link on how to handle MA just in case you are not familiar with it: http://www.poolforum.com/pf2/showthread.php/13111