(If you're in the US)
I'd say "call ahead and make sure they have it in stock" but that's impossible. Gotta walk in and ask. This includes if you're uninsured and you're doing the bridge access program thing.
You can check on vaccines.gov to see if the stores near you are supposed to have Novavax and if they do bridge access, but to actually get it you just need to walk in and get it. It, like seemingly everything medical related nowadays, is in short supply, so you may make the trip and find out you have to come back another day. Such is life.
I just assume everything requires an appointment and telling someone in advance that you aren't supposed to pay lest they charge you a bunch. Medical access in the US is fucked and it's very strange when you can just... walk in to a place and get medicine, that everyone needs, for free.