Try this website:

http://www.stagonset.co.uk/fasteners?cart_id=556713_32052&prm_grp=A2_PClip_RbbrLnd&summit=Stainless|Steel|Rubber|Lined|P|Clips#top

There not exactly the same, but I think they could quite easily do the job. Dirt cheap to and a whole heap of sizes available.
Ive never used the site before, but I did see it advertised in a magazine (Classic Bike I think it was).

Or why dont you just bond the hanger directly to the silencer? Would make removing them a bit of a pain, but would probably be lighter (and even cheaper!).