Yes, they have all the boosters. Go online to the Costco site to register. You can also just stop by the pharmacy and ask if they have any last minute openings.
Right now Costco is having you make an appointment on their website, and it is done through a third scheduling party. The system will link you to that scheduling company after you give them permission, and if it says that the "resource is unavailable", that means that it is already pretty well booked for that time. There are cancellations daily, so if you call the pharmacy and tell them if you have any problems, they will usually assist you as well. They have all three companies for boosters, Pfizer, moderna, and Johnson & Johnson. Good luck!
Costco does offer Moderna boosters, I got one there. Scheduling an appointment is difficult right now but if you Google Costco covid vaccine, it should being up a link to their page to try to schedule an appointment.
Thanks! Your answer is awaiting moderation.