It's really easy to make your own celery salt from using celery leaves and table salt, Kosher salt or sea salt.
All you have to do is to harvest celery leaves, wash them if they are dirty, dry them as much as possible with a clean dish towel or in a salad spinner and and dehydrate them.
To dehydrate, your celery leaves, either use a dehydrator or use your oven.
If you are using an oven, preheat to 350°. Line a baking sheet with parchment paper and lay out your celery leaves in a single layer. Cook for 5-10 minutes or until the leaves are crispy and before they get brown.
Once they cool, crumble them up and mix with an equal amount of salt. Store in an airtight jar.