There is no official store, and the official project does not reference any third-party vendors.
You do have options:
1. Do you want to buy a third-party device like a NitroPhone? If you can afford to purchase a phone in the first place, then purchase a used phone to try flashing GrapehenOS. You can buy multiple used devices for the cost of such a device, and then you can familiarize yourself with the flashing procedure.
2. Have a friend help you. There are probably events in your town that you could find on Facebook, Reddit, or Meetup (e.g., OS install parties are a thing).
You do have options:
1. Do you want to buy a third-party device like a NitroPhone? If you can afford to purchase a phone in the first place, then purchase a used phone to try flashing GrapehenOS. You can buy multiple used devices for the cost of such a device, and then you can familiarize yourself with the flashing procedure.
2. Have a friend help you. There are probably events in your town that you could find on Facebook, Reddit, or Meetup (e.g., OS install parties are a thing).
3. Wait for the official project to begin selling their hardware: https://twitter.com/grapheneos/status/1490518600339308544