It is possible to punch a product name and a post/ZIP code into a search engine to see where it's sold in your area. I've done this with A&H Washing Soda and Bell's Poultry Seasoning with success, as my nearest supermarket carries neither and doesn't seem interested in starting to.
I agree that washing soda has not been seen in most US supermarkets in some time. I found borax in the laundry section of a Target a few years ago, not sure if they still carry it.
More importantly, I would like you to share which developer recipe uses Bell's Poultry Seasoning!
