I highly doubt that the 2006 ROBLOX client was found, all of my researches i had done on the 2006 client were just modded versions of March 2007 clients, the 2005 version of Dynablocks (including the oldest version found, GoBlocks from 2003), it was supposedly "found", as i stumbled upon an April 1st joke video by GroovyDominoes52. So i'll flag these 2 versions as lost for now.