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I found this site on cleaning gravestones and it lists a few specific nonionic cleaners http://www.savinggraves.org/education/bookshelf/non-ionic%20Detergents.htm
Triton x-100 is available here http://www.2spi.com/catalog/supp/triton-x-100.html
Here are shopping results for Tween 20 http://www.google.com/products?q=tween+20&ie=utf-8&oe=utf-8&rls=org.mozilla:en-US:official&client=firefox-a&um=1&sa=X&oi=product_result_group&resnum=4&ct=title
Photo Flo is available on Amazon http://www.amazon.com/Kodak-1464510-Photo-Flo-Chemistry/dp/B00009R7E0
Hope this helps.