This is a user to user only forum. Since none of us are in any way tied to Apple, we couldn't possibly know anything about Apple inventory. One can well imagine with supply chain issues around the world and a shortage of chips worldwide, that must have something to do with the supply of the model you are interested in.
Otherwise, feel free to use the Get Support button at the top of this page to ask Apple if they have sense of when the model you want may be available to be purchased.
I do have a question however. Have to tried to order the model you want? You may not be able to just walk into an Apple Store and walk out with the version you want, but typically, you can order what you want and it will be delivered when available.