When I was making and selling custom wood arrows it was no trouble putting together weight and spine matched groups.
I typically bought shafts at about 200-300 each per spine group. Every shaft got spined and weighed by me and the spine and weight was written on the end of the shaft. Laying the shafts out on a table with lighter weights on the left going to heavier shafts to the right it was easy to gather together bundles of 12 shafts that were within specs for weight. Any shaft found to be out of spine for that group was put into the correct spine group. It wasn't at all unusual to have a few dozens that were the same spine and within a couple grains of one another for weight; those were well matched dozens.
When building the arrows it was pretty simple to keep the weight of one arrow the same as the others to end up with matched sets.
Guy