Pretty sure I dropped the key in the parking lot for Stairway to Heaven in Eureka, Colorado yesterday (2/18/22). I’ll be back in a few days if anyone happens to come across it!
The code on the lock cylinder is only visible after you extract the lock core/cylinder, which requires the lock to be open. Lots of Yakima dealers have a master set of keys that they can go through to find a key that works, then sell you a key with that number. The master set won't be for sale, but at least you'll know the key number so you can buy a new key from someone who has it in stock. Another option is to extract the lock core that you lost the key to, and buy a new set of locks and keys. Yakima keys are subject to the same supply chain issues that the ret of the retail world is seeing, so don't be surprised if the key that fits your lock is unavailable.