If your looking for the RGB equivalent of a paint swatch, your probably better off looking at Pantone colors.
You can buy Pantone swatches (I think their pretty expensive though) and then use Photoshop or something to find the equivalent RGB value.
If you go into Photoshop and click on the Color Picker in the toolbar, theres a Color Libraries button that'll show you a great many Pantone colors. Click the one that matches the printed swatch and when you go back to the color picker, you'll see the RGB value.
As wikipedia says, Pantone is pretty much an industry standard, used in painting, printing, etc...
I'm sure you can in turn give a Sherwin Williams or whoever and Pantone color code and have them mix paint for you (if thats what you want).
If you want to take photos of the room you want to paint, photoshop it with the color you want from a swatch, some of the websites (we used sherwin williams) have tools to do that also, but won't produce Pantone or RGB values :(