I'm pretty sure I read somewhere a cool 4th-level wizard spell whose name was Burst of Frost and Flame, but I can't find anymore which book it was in, and I have too many PDFs to search one by one! Someone please can put me on the right path?
There's a list of (all?) 3PP spells on PFSRD: https://www.d20pfsrd.com/magic/3rd-party-spells/
Such a spell is not among them, though. Do you remember what it did? Maybe you meant Body Heat Ray?
Those are nowhere near to be ALL of them ^_^ and no, I already had searched there before posting...
Not one of mine, sorry.
a cool 4th-level wizard spell whose name was Burst of Frost and Flame
Again, if you want us to be able to help you, you need to provide some additional information. Nothing turns up on the name "Burst of Frost and Flame" at all, and the only other information ("cool", "4th level wizard spell") is a little weak. Do you remember what it did? Did the spell have unusual targets, durations, parts in its description, a rare descriptor (e.g. calling, poison)? What was "cool" about this burst of flame? Was it a rare colored flame, did it look like gnome's hair? Anything?
The 3e Warmage has a fireburst spell that damages adjacent targets.