https://www.wow-professions.com/guides/cataclysm-engineering-leveling Here is a list of all the mats you require to level cata eng up to 75....Volatile Fire can be obtained from veins, I would just farm the river bank in Twilight Highlands, and Volatile Air can be obtained from Sealed Crate
https://www.wowhead.com/item=78930/sealed-crate . This is fished in the pools on Darkmoon Faire island, but I dunno if those pools still drop the crates (Need confirmation).
Only problem is that you will need for the Darkmoon Faire to begin, and only got 1 week to farm the 30 Volatile Air required (2% chance to drop). The other way would be to farm
https://www.wowhead.com/npc=46328/enslaved-tempest in Twilight Highlands, but with help from other twinks. If you do all this, you can acces the cogwheels gems from the vendor (In SW for Ally, dunno for Horde). Be warned the cogwheels require eng crafted items. Hope this helps, but all this info is more of a larger tip, is by no way fully complete.