The Planar Edge

This was trainable from Weaponsmithing trainers, but Blizzard "forgot" to move the spells to general BS trainers when they removed the specialities.

Vey nice main hander, i will surely go for it when reaching 70.

Expensive mats though, the core requirements are
24 eternium bars
36 fel iron bars
20 adamantite bars
20 primal shadow
5 primal might

If buying this on EU/Frostmane it will cost you about 780g, but the only thing unreachable by a blacksmith is the primal mights.

Gather the required mats for 5 mights which are
50 mote of fire (http://www.wowhead.com/?item=22574)
50 mote of air (http://www.wowhead.com/?item=22572)
50 mote of water (http://www.wowhead.com/?item=22578)
50 mote of earth (http://www.wowhead.com/?item=22573)
50 mote of mana (http://www.wowhead.com/?item=22576)

Make primals of the motes (just right click them) and sell them at the ah for about the same price as the mights would cost you.

As a blacksmith you're probably also a miner. None of the metals are really hard to come by. You should have more than enough at the time you have collected the motes, except maybe eternium bars which can be bought for around 1g each in the ah.

A wild guess is it will take 1-2 days of farming in various places to gather all the mats for this axe, if you're 70.

Start collecting the mats as soon as you hit 58 and go to Outland.
In the first area, Hellfire Peninsula, you can gather mote of earth (in many mines), mote of fire (in some mines), mote of shadow, Fel iron ore and possibly some eternium ore.
Mote of water is quite is farmable in Zangarmarsh.
Adamantite and more eternium can be mined in zangarmarsh, Terokkar forest and all the other higher level areas.
Mote of air and fire in Nagrand.
Mote of mana is the most difficult, i have yet to find some.

Kirin'tor(sp?), that place in netherstorm with all the ghosts has a great droprate on motes of mana. I farmed about 4 primals while completing the quests there.