I'm not the best one to speak about this, but I have had some experience. If there are any graphic artists or print shop owners, they might be able to help out better.
Back in my day, high school journalism - that is. When we would submit the newspaper to be printed at the local shop, they would request a Pantone sheet of values follow along with it. This sheet would identify all of the colors that were used in the paper. What I'm getting at here, is that along with colors, Pantone also made provisions for percent grey. 5, 10 you name it. We could pick the color from a "wallpaper" book if you will, and they would print the exact same color, except on crappy ol newspaper. We used Adobe Pagemaker back then and it had the complete pantone color chart available.
On a side note, this might work out well for all of the people in HT land that have nice ink or laser printers that could print a sample to view in their HT.
Does someone what to create an Adobe Acrobat document with all of the values? Then a user could download 20% references, narrowing it down to 10% then 5% - till their happy....
I haven't checked to see if HD or Lowes can match pantone colors, but some of the graphic people might be able to say what's up.