In my experience Costco tends to offer DJI drones only after several months after they have been officially released. For example the
Mini 2 was released Nov. 2020 but Costco didn't have their package for sale until maybe April-May 2021. Same goes for the
Air 2S, it was released April 2021 and I only started seeing this Costco package in October.
Mavic 3 is most likely coming out in October. But for these reasons I doubt Costco will have it anytime soon. They may not ever sell it as it's higher-end and I don't recall e.g. whether Costco ever sold a
Mavic 2 pro package. They tend to sell the ones in the range of e.g.
Mini 2 and now
Air 2S.
Same goes for the
Mini 3 - if the rumors are true this may come out in Nov. 2021. But again if it does come out don't expect Costco to offer it until sometime 2022.