Binding Barrel Bolts at Grainger...
I don't see any in hex, but check this category:
http://www.grainger.com/category/bolts/fasteners/ecatalog/N-8jp?cm_sa=true
And for example, one in 3/8-16 thread...
You're going to "try" explosive welding this weekend?
Be sure to have someone hold your beer and record video of the event. I'd like to see the aftermath.