All my gardens are laid out in sections of 4 by x feet. The picture shows 2 areas that are 4 x 12 feet in the front of our house. I then divide those into 2 x 2 foot areas. I number and label the area with 1 x 12 inch paint stirring sticks. I use Quickbooks 2013 to keep track both inventory and sales. There are 5 "Custom Fields" you can set up for each inventory item. I set one of them as "Location". The picture shows 2 4 x 12 foot areas, they would be labeled FR - 01 thru FR - 24. Our back yard has most of our inventory and is laid out in a similar fashion. I can then use Quickbooks to print inventory lists sorted by name or location or any other field i want.
We really don't sell that much, just enough for the gardens to pay for themselves. It is a lot of initial setup work but it really pays off when finding specific iris to dig and ship.
Hope this helps.