Did you read Pub 526:

https://www.irs.gov/publications/p526

"If you contribute inventory (property you sell in the course of your business), the amount you can deduct is the smaller of its fair market value on the day you contributed it or its basis. The basis of contributed inventory is any cost incurred for the inventory in an earlier year that you would otherwise include in your opening inventory for the year of the contribution. You must remove the amount of your charitable contribution deduction from your opening inventory. It isn't part of the cost of goods sold.

If the cost of donated inventory isn't included in your opening inventory, the inventory's basis is zero and you can't claim a charitable contribution deduction. Treat the inventory's cost as you would ordinarily treat it under your method of accounting. For example, include the purchase price of inventory bought and donated in the same year in the cost of goods sold for that year."