I have managed to get every spell apart from the 2 from Baelfyrs. So far the only place i have seen fire weather was once in Moh Gates.
Adoulin spots that can have fire weather, according to friends and people who've posted on the forum:
Ceizak (rare)
Yahse (rare)
Moh Gates (fairly rare)
Your best bet is probably Alluvion Skirmish Yorcia (tier 3 or higher) with some friends. Not incredibly hard once you got a good army going.
I did this myself 3 times now and learned Searing Tempest on the 2nd run. Still no luck on Blinding Fulgor though...