Michelin Ultra Heavy Duty Rear Inner Tube 100/110/90-19 100/110/90-19" TR4 Valve 4.00mm Thick Fits Rear 100/90-19", 110/90-19", 120/80-19" and 130/70-19" Tyres.  

Pirelli Heavy Duty Front Inner Tube 3.00-21 / 80/100-21 / 90/90-21 Pirelli inner tubes are a good heavy duty inner tube. Available in a multitude of sizes.

Michelin Heavy Duty Front Inner Tube Trial 2.75-21 2.75-21" Special Trial TR4 Valve Fits Front 2.75-21" Trials Tyres. Heavy Duty Reinforced Inner Tubes are 2.5mm thick. 

Michelin Heavy Duty Front Inner Tube 80/100-21 80/100-21" TR4 Valve Fits Front 2.50-21", 2.75-21", 3.00-21", 80/90-21", 90/90-21", 80/100-21" and 90/100-21" Tyres. Heavy Duty Reinforced Inner...

Michelin Heavy Duty Rear Inner Tube 110/90-19 110/90-19" TR4 Valve Fits Rear 110/90-19" and 130/70-19" Tyres.