This seems to be a Country specific, and then a geographic issue in the US.
From what i've read here, Countries outside of the US have no problem walking in most of the time to any store and buying one.
Here in the US, it seems to be a mixed bag. I can tell you for certain, that here in Central Texas you can't just walk in stores and find them yet unless you happen to get lucky and stumble in within a day of a stock refresh. I had to get mine in a Best Buy Online drop a couple weeks back.
I'd say for US buyers for now, if you want to avoid the annoyance of going into store after store and finding nothing, your best best will be online drops at Best Buy and/or Walmart. Follow Wario64 on Twitter/X, and you'll know with plenty of leadtime when the drops are. I saw in the last day or so that Amazon US finally put them online but you have to request to be able to buy one via something you'll click on the product page. No doubt priority will go to Prime Members.