I made mine from the shredder provided, but I know that's not a very popular method. I believe there's some tutorials on using the dark lance and blast pistol, but that just seems wasteful. The 'best' option I've found is to just buy extra, from places like bitz or the like.
I don't remember the rules on links to other sites, so I'll err on the side of caution, and just say that Archon 3D Smiths is a very good site for finding things aeldar related that you don't want to buy 4 boxes for: scourge weapons, raider->ravager conversion bits, helmets, and of course, blasters and special weapons