Up for sale is this standard sixe,  Zoo Med Repticare Rock Heater:

This is a new in box, sealed, and features: Item RH-1

• Hydrated rock material, twice as strong as cement or pumice
• Conducts heat evenly with no hot spots
• Water resistant element with washable surface
• UL listed for safe operation
• Works with all types of Snakes and Lizards including Boas, Pythons,Rat Snakes, Monitors, and Tegus
• Full coverage, completely encapsulated heating element