Heated ceramic piece to high temperature (>200) to radiate FIR
Lamp with near-IR optical filtered halogen bulb
Use industrial FIR heater in the sauna house
Add far infrared material (carbon or Ge) to fiber or fabric clothing products
Add few (<1% ) far infrared material (carbon or Ge) to fabric protection gears
Salt crystal, crystal or titanium will radiate low power far infrared