Joe comments

Have the entertainment industry take over. They can sell "tickets" through the usual means, like email, convenience stores, or by phone. They understand crowd control, how to set up lines, how to check ID and so forth. They have large, mostly empty spaces with access to good transportation. Have them add personnel from the tour industry to act as "ushers" and to explain the procedure and answer questions, and to pre-screen the customers for allergies, etc. The actual shot giver would then only have to have a short chat before the jab, and be ready for another customer in less than five minutes.

If I was in charge, I'd work with the entertainment industry. They would handle the "ticket sales" (appointments) and direct people to the nearest music venue/vaccination site. They understand crowd control, have large spaces, and plenty of under-employed staff.

In Seattle I went to the Amazon "supervax". From the parking lot on, there was a volunteer every 30 feet. After entering the main building the first stop was a temperature check, and then several "ticket takers" to confirm appointments. I got a wristband to indicate I was a legal entry. There were distancing markers all the way along the adjustable queue lanes, leading to several pre-shot consultation and questionnaire stations. Another volunteer directed me to one of around 50 injection stations, the available ones waving little flags. I had another brief consultation, got any remaining questions answered, a jab, a card with a vaccine lot number sticker in the "first dose" box, and a sticker showing the time (15 minutes later) I could leave, then was directed to the waiting area, featuring a large clock. Then more volunteers and signage showing the way out. There was even a staffed "selfie station" with a large sign saying: "I got my vaccine!" All in, it was an hour.

The only tricky part was various outlets having separate reservation websites, but I think they've been consolidated by now.

Use them for nuclear waste storage.