These are a giant pain in the ass. When I leveled up my enchanting there were 0 of these bars up at the Auction House, and I'm sure if there were any I'd pay almost anything for them. These are needed to craft the Arcanite Rod which is a necessary component in order to level enchanting.
In order to craft the Arcanite Rod, you need 3 arcanite bars, not only that but you also need to go get the formula which can be bought in Moonglade ( really? What the hell Blizzard, why Moonglade? ) Neither the raw arcanite rod nor the arcanite bars were at the Auction House at the time that I needed them, the demand was there, but the supply wasn't.
These are two tips are great examples of how to passively increase your daily gold making income. You can craft multiple of the bars and snag a couple of the formulas and just throw them up whenever you're near the AH and this will help you make gold passively.
The demand for the bars and rods is out there, the question is will it be you supplying them? Or will it be the guy right next to you?