When to start stocking up

So this will be my 3rd little human, and so far I have yet to be able to Brest feed with out supplementing with donated milk or also have formula. If this was the Middle Ages I’d be looking for a wet nurse. They’ve done checks and I’ve seen lots of lactation consultant and specialist, all to find that structurally there is nothing wrong my boobs there just lazy and can’t seem to figure out how to have enough supply to keep us out of the danger area for baby. (Yes we have also looked at latch, hold, mouth shape vs nipple shape and anything else that came to mind, I’ve also tried the supplements, teas and bars and milk production snacks and any other random thing that seemed helpful) I’ve come to terms with it and it doesn’t cause me distress anymore.

My thing is what seems like a good time to start stocking up on formula? Thankfully my other 2 didn’t require special formula but I’m concerned if I start too soon then this new little one will need something I didn’t buy (cause that’s what happens when you plan)

Anyone else have a similar dilemma?