So what I have found is it doesn’t matter so much how much you buy, but how often you frequent the store and then also store selection. Like IMHO your better off spreading your budget over the year as opposed to maybe making a few big purchases when store wide sales come around. The store managers typically reward regularity over one large one-off purchase.
I would also recommend getting to know who handles the allocated products (wine/whisky/whatever) and get to know them and then make a point to chat with them every time you are in the store. They are more likely to help out their “friends”
Lastly I think store selection plays a big part in this as well. It’s always better to be a big fish in a little pound if at all possible. Since it is impossible keep up at the spending levels of super high end stores regulars.
Obviously this takes a lot of work and you will have to put in a good amount of time, but this is how I have managed to get allocated stuff from a few different places.