Gnomish Power Goggles are crafted by Engineers with a skill level of 375 who also have the Gnomish specialty. As they bind on pickup, the only way to get a pair of these goggles is to be a Gnomish Engineer and make them yourself.
The schematic can be learned from Gnomish Engineering trainers (Tinkmaster Overspark in Ironforge for Alliance or the neutral Oglethorpe Obnoticus in Booty Bay if you're Horde). You cannot learn this schematic unless you have specialized in Gnome Engineering.
When it first appeared in the Burning Crusade expansion, this schematic required Spellfire Cloth rather than Spellcloth. However, there was no such thing as Spellfire Cloth (it had been renamed to Spellcloth during the expansion's beta test), so it wasn't until the next major patch (2.1) that it was possible to craft this item.
However, many new epic-quality Engineering goggles were introduced at the same time that required only 350 Engineering skill to make and could be learned at any Engineering trainer, without any specialization required. These require to craft, limiting their quantity.
These Power Goggles requiring higher skill, specialization, and expensive materials - but no primal nether.