Joe,
Vicki carries nearly all of the Bainbridge and Crescent lines. She has everything you really need.
Go through your samples and sort them by color-wheel colors. No beige or brown, please. Bainbridge labels all their new samples according to color wheel references and there is a list available to label older samples. I've gone through and labeled the Crescent, TruVue and Artique mats as well. Let me know if you need a list.
Then look at all the samples in a group - say, the red tints. You'll notice that several mats from the different manufacturers are either identical or close-enough for government work. Pick the one from your favorite line, and continue.
You know what you use. If you like neutrals, you might want 20 different whites and another 25 grey tints. Just make sure they're different. And you'll want a few from each color wheel group. I use 41 groups.
If you decide you have room for 600 boards, and you get weekly delivery, you probably only need 1-2 of each board, so pick 300 representative colors. You can add or subtract to the stock selection as you fine tune it and new colors come out. And don't try to save every little cut-off piece. I save only one partial sheet of each color and it needs to be 32" high so it doesn't get lost or clutter up the bins.
Sorry to be long, but this is a (very odd) passion of mine.