I've purchased a lot of paint and I can say I understand the frustration. My local paint shop seems better stocked in terms of chip books than others I've been to. I've been to some shops where they only have one sample book and if the color wasn't in the book you weren't going to get paint. The unfortunate part is that as good as my shop is about having paint chips to compare there is no secret formula such as bringing in different color codes they can input and out comes the right paint color. When I'm painting I do as Andrew has suggested and tell the client find a car color you really like, that is the best way I can ensure the color will meet the expectation. I have had a more than one occasion where I went in with a color on my phone and tried matching in to a book only to find later I was sanding and picking a new color. Best of luck!