they should have it at an auto parts store... get the lowest temp you can (most likely 180 degree)
To change it on an LT1... take off the intake duct by loosening the two clamps that hold it on... then you need a small socket wrench (10mm?) for the two nuts on the T-stat housing... BE CAREFUL not to let too much coolant drip down (none is better, surround with rags if you can... this is to protect the opti spark) from here, just pull up on the stat, and replace with the new one the same way... put everything back together, open up the two bleeder screws until coolant comes out steady... top off the coolant, start it up and test out