you probably want to look for a canvas or nomex shell, depending on your budget, then combine that with a gore-tex or event liner, and wear one of the FR fleece liners inside that. Or just wear a rainshell over your FR stuff so that if it does burn, at least you won't have it melted to your skin.
All depends on what your major risks are, and your normal operating conditions. at -30 layers are the way to go already, but I'm sure you knew that.
factors that make things water resistant tend to be flammable, and fire resistant stuff tends to not be waterproof.
Wool is an option, wool also gets very heavy and wouldn't be the best choice for standing out in the rain all the time. But at -30 rain isn't much of a problem. So not really sure what you are trying to solve. If its some sort of major fire hazard then nothing but fire-fighter gear will do, as its important to block the water from getting to you, so you don't flash-boil yourself in your suit like a lobster. "Normal" FR clothes are more to protect against sparks, flashes, and keep the fabric from being melted to your skin.