Many hardware stores/home improvement stores do not carry rockwool. Your best bet is to go to the manufacturer websites, they have 'locators', where you can enter you ZIP code to find nearby suppliers. [hotlink removed by Zillow moderator.] You may have to make a special order to get the batts you need.
[Promotional hotlink removed by Zillow moderator.] should cost next to nothing. Just drain out the reservoir, drain out the water line, replace the pad, unplug the unit, and cover it up.