Local vet here has a standalone box for collection of medication, might yours be open to a similar suggestion?
i would avoid frontline, fipronil is an aging chemical, most flea jobs i do are at houses that have been using frontline
Farmer's suppliers are still open, but you may need to phone first (or when you arrive).
Vets are doing emergency stuff only, but if you need anything, and you are an account holder, phone and they'll leave stuff out for you to pick up.