You can sharpen Iceblade, Lifeblade and Deathblade to 50% using the Sun School spell Sharpened Blade spell that you can learn at level 86. Storm has Supercharge that creates a blade of 10% per pip so it can be up to 140%. Other than those there aren't any blades 50% or larger.
Actually, there are usable blades that are at least 50% but they are only useable in the battle you find them in...you have to steal them from the bosses that weild them. It happens all the time when battling the loremaster.