Trainer Schematics
If all you want from the engineering profession is to get to the maximum possible skill, you needn't look any further than your local engineering trainer, who will be happy to teach you a variety of schematics appropriate to your skill level. As your skill increases, you will be able to learn more complex schematics, so speak with your trainer regularly.
Vendor Schematics
Vendors all over the world may have engineering schematics available for you to purchase. For example, Xizzer Fizzbolt in Winterspring will occasionally sell schematics for the Delicate Arcanite Converter, Fused Wiring, Gyrofreeze Ice Reflector, Masterwork Target Dummy and Powerful Seaforium Charge, while Wind Trader Lathrai, in Shattrath City, may sell schematics for the Fel Iron Toolbox and White Smoke Flare. Some vendors always have schematics available in unlimited quantity, while others sell only one or two copies of a schematic at a time and restock only rarely.
World Drops
Certain schematics may drop from any enemy of the appropriate level in the world. This category of schematics includes fairly common ones, such as the Mechanical Squirrel and Catseye Ultra Goggles schematics, as well as extremely rare ones, such as the Arcane Bomb, Sniper Scope and Craftsman's Monocle schematics. Although you may be lucky and find some of these schematics while killing enemies, your best bet for obtaining them is to regularly check the Auction House for available schematics, as non-engineer players who find them will often list them there to sell them.
Dungeon Drops
Some engineering schematics are held by enemies found deep within dungeons. For example, most bosses in Molten Core can drop schematics for the Biznicks 247x128 Accurascope, Force Reactive Disk and Core Marksman Rifle, while Attumen the Huntsman, in Karazhan, holds the schematic for the Stabilized Eternium Scope. Enemies in Sunwell Plateau have a tiny chance of dropping exclusive goggles schematics, while enemies in Blackrock Depths may drop the schematic for the Dark Iron Rifle, Dark Iron Bomb, Gnomish Alarm-o-bot, Goblin Jumper Cables XL and World Enlarger. Mekgineer Thermaplugg, in Gnomeregan, can drop a wide variety of schematics, including the one for the Pet Bombling companion, while robots in the same dungeon have a chance of dropping the schematic for the Lil' Smoky companion.
Location-Specific Drops
Certain engineering schematics drop only from specific enemies. For example, the schematic for the Felsteel Boomstick drops from Sunfury Bowmen in Netherstorm, while the schematic for Hyper-Vision Goggles drops from Mo'arg Weaponsmiths in Shadowmoon Valley and the schematic for the Field Repair Bot 110G drops from Gan'arg Analyzers in Blade's Edge Mountains. Most of these schematics bind when picked up and will only drop for engineers, although some low-level ones, such as the Flawless Arcanite Rifle schematic from Mossflayer Shadowhunters in Eastern Plaguelands, drop for all players regardless of profession.
World Events
During the Lunar Festival, a yearly event that coincides with the Chinese New Year celebrations, you can purchase several engineering schematics that are otherwise unobtainable. The schematics are sold by Fariel Starsong, in Moonglade, in exchange for Coins of Ancestry, a type of currency that you can obtain by visiting Lunar Festival elders scattered all over the world. You can purchase schematics for the Cluster Launcher and Firework Launcher for five Coins of Ancestry each, as well as recipe packs containing schematics for green, red and blue versions of Large Rockets, Small Rockets, Rocket Clusters and Large Rocket Clusters, for an additional five Coins of Ancestry per pack. To purchase all available schematics, you need Coins of Ancestry.
Reputation Factions
Obtaining certain schematics requires you to increase your reputation with a specific faction. For example, Alliance players wishing to obtain the Mekgineer's Chopper schematic must reach exalted with the Alliance Vanguard, while Horde players wishing to obtain the equivalent Mechano-Hog schematic must reach exalted with the Horde Expedition. The Elemental Seaforium Charge schematic requires you to be revered with the Consortium, while the Green Smoke Flare schematic requires you to be friendly with the Cenarion Expedition.
Quests
Some engineering schematics are rewarded by quests or sold only by vendors unlocked through questing. Zorbin Fandazzle in Feralas will sell the Snake Burst Firework schematic to players who have completed his quests. Similarly, Damek Bloombeard in the Molten Front will only appear for players who have unlocked the "Additional Armaments" stage of the Firelands invasion event. The Zapthrottle Mote Extractor schematic is rewarded by a quest in Zangarmarsh, started at Teldredor for Alliance players and at Zabra'jin for Horde players.
Salvaging
One schematic in the game, the one for Jeeves, is only obtainable through salvaging the corpses of specific mechanical enemies. You can obtain this schematic by salvaging any mechanical enemy found in Northrend. The higher the level of the enemy, the higher the chance of you finding one: Flame Leviathan, XT-002 Deconstructor and Leviathan Mk II, the three mechanical bosses in Ulduar, have the highest chance of dropping this schematic when salvaged.
Discoveries
When crafting any engineering item that was added to the game during the "Cataclysm" expansion, you have a chance to discover the schematic for one of eight possible tinkers you can apply to your gear. These tinkers are the Synapse Springs, Cardboard Assassin, Tazik Shocker, Quickflip Detection Plates, Grounded Plasma Shield, Z50 Mana Gulper, Spinal Healing Injector and Invisibility Field.