This site has a plethora of model instruction sheets. All makes, scales and genres. It may not contain every sheet in the world but there is a schwack of them.
Main instructions site : KIT INSTRUCTIONS - Revell, Italeri, Fine Molds, Polar lights, Hasegawa, Trumpeter, Academy and more...
I've often wondered about the nature of the various products I use when modelling and have thought about obtaining Material Safety Data Sheets (often known as MSDS's) for them. I've never gone to that step yet until today, when I accidentally stumbled across this site that seems like a handy...