Often common household products are as dangerous as chemical hazardous wastes: if you don't understand their dangers, properties and how to use them safely. Unfortunately, the Department of Labor (DOL/OSHA) rules are aimed at the workplace, not the home, so technically, there is no requirement for an MSDS to be provided for household products (unless they are used an OSHA-defined "workplace, and "domestic engineer" doesn't qualify for that). So, some manufacturers of consumer products (home and garden), have taken their MSDS's off the internet. For example, for "Roundup" (tm) Monsanto's website says:
"Sorry. We do not list Material Safety Data Sheets (MSDS) on our Web site. Call the number on the label for more information. Please be prepared to provide the exact name of the product (as it appears on the label"
That being the case, if you are looking for the msds for a household product, you may want to try the household products search first. These free (but copyrighted by a private company) data sheets from the National Institute of Health provide health and safety information, ratings of the hazards of the product, name, address and phone numbers of the manufacturer, and even chemical composition and ingredients. You can use this information to evaluate the product, and compare it with competing products to choose a product that meets your needs but is less dangerous to you and the environment.
In addition to the household products safety database, there is quite a bit of useful information about household poisons and other household safety issues on their website.