Can the planks of Black Ash Heartwood only be used for Bree-spears? And how hard are Elven Blades to come by? Suppliers doesn't sell them, and I didn't find any of them at the AH today.
The blades are crafted by a weaponsmith. You'll have to make an order with someone to get them most likely. Ask in /trade or even /glff for someone to make them for you. As far as I know, black ash heartwood is only used to make bree spears.