We used to SRML wire, which I understand is "Silicon Rubber Motor Lead" but I'm not sure about that. The environment was an ice cream freezer in a dairy where the temperature was -40° F. The problem was THHN wiring would get brittle and the insulation would just snap right off when you tried to bend the wires. My question is twofold. Is there any other wire that we could use for this temperature environment and what is the temperature rating for SRML wire?

It seems suitable from the temperature standpoint
-60c to 180c (some brands are even more wide ranging)

http://www.alibaba.com/product-gs/210084293/JG_Silicone_Rubber_Insulation_Motor_Lead.html

The open question is if it is only listed as fixture wire or is it an chapter 3 conductor.

I looked at this a little more. I would probably be OK with the idea of these conductors in pipe but you have to watch the terminations. This is nickle or nickle plated wire so the splicing devices and terminals have to be OK with that.