Another source of sponges I have come across are from nautical/sailing equipment sites, such as the one linked below. I haven't enquired into how sterile they are, but they do come under "survival" equipment. I'm sure there must be similar US based sites.

http://www.sailgb.com/sshop/prod_info.asp?pid=12182

Hope it helps
Martin

Nope, no horns, but someone did write "wash me" in the dirt.

Ever since I read that article, a pair of 3M sponges has been part of my kit. But the kit has always included a couple of PackTowl's...one smaller one cut into washcloth and hand towl sizes, and one bath towel sized. I thank Douglas Adams for this...never leave home without a towel.