Well Rob like they always told me you have to walk before you run and the rudiments of any aspect of blade making or throwing is always interesting to me!

 

  There is so much scrap steel out there that you should be able to find something that is already hardened (just my personal opinion), leaf springs, replaces bottom edge of a snow plow blade or any of a number of things may work for you?

 

 I would try to keep the knife close to the same width in the handle as the blade because it will be an easier transition to throw by the blade or handle, 12" to 16" is Conventional Tournament Standard and nowider than 3"  at any point.

 

 Hope this helps a bit!!!

 Joe D.