I found rivets that were long enough on ebay, but as BR said, hard to set without destroying things.  I was trying it on an already cracked and very much sanded model 92 handguard.  I really wasn't set up right, didn't have a vise and it wasn't long till the handguard had another crack I'll have to repair!  That project got set aside, and I wonder where those rivets ever got to?