Answered Hot End Temp Sensor Replacement.

any RepRap style 100k thermistor will work.

https://www.amazon.com/RioRand-10-100Kohm-NTC-Thermistors/dp/B00GD471PO

Choose 100k EPCOS as the thermistor type in the firmware for that one

Look around,that was the first one I found.
Probably better prices out there and maybe less if you don't need spares.

Here are some already wired up

https://www.amazon.com/HICTOP-Thermistors-Sensor-Reprap-printer/dp/B0150YLX9C

(they say type #5 in the marlin firmware for those)

 

I cant find those aftermarket. I asked robo for a replacement and they sent 2 free under warranty.

The r1+ thermistor is a wierd beast

 

Yes, they are continuing to add more custom parts to the printers as they go (which does not bode well for the R2).
Still, as long as they are competitive on replacement part costs...