Not sure this is possible without having an external server resource - however i'm happy to be proved wrong.You can mimic the pickup_availabilty files, which gets the   .store_availabilities array, showing whether a product is available at that locat...

i've joined just to say thanks for this, after changing from an admin api to the storefront, it would've taken me hours to find this out had it not been for your post showing up in google.