Here are some suppliers, generally cheaper than the kiln manufacturers/dealers
Mitsco thermocouples - good value R and K thermocouples
Avery Weigh-Tronix thermocouple calibration - inexpensive calibration, but to a low temperature for kilns
Sterling Sensors - wide range, but R/S are very expensive
TMS Europe - thermocouples, loggers, ceramic tubes etc.
Omega - thermocouples and many other sensors and loggers
RS - data loggers etc.
Thermocouple - Fix it before it fails