Rune mages availability

[Hyvel]

You could also use the console to give yourself the old shoes: name of the item would be 'old_boots', without the quotation marks.

[Doombrew]

I didn't know about the spell "Sacrifice", but it looks like something you could use.
In other cases their might be Rune Mages in the enemies army - With the Diplomacy Skill from the Mind-tree you could be able to get them to desert and join your army.