Hmm, I am thinking of the old leather cuff guards Duke Wayne used to wear. A good piece of soft split suede under a piece of thin laquered rawhide, with a piece of 3 oz calf or goat skin over the outside, laced up on the inside, about 4 inches wide. The lacing allows for an almost infinite custom fit. Tough, yet flexible. May not hold up to a smashing knife strike or a hard thrust, but ought to deflect the usual slash strokes. I suppose you could put some cartridge loops around the outside or some such for mounting acourterments.

You could also braid some rawhide and piano wire into a bracer of sorts, that would be much more impervious, but a bit more bulky.

I'm even thinking you could braid some 550 cord into a sort of bracer with all sorts of things wove into it.

Hmm, the more I think about it, the more I like the braiding idea...