For those wondering which Wave 5b amiibo they should prioritize to get in America, I'll be telling you which are most likely to be gone first. I cannot guarantee that it'll happen exactly like what I said, but it's just an idea based on how scarce they are elsewhere. I do have to mention that these amiibo have longer production time compared to the previous wave, so it's going to take a long while for these to go out of stock. I checked reddit's obtainability chart and so far, Europeans didn't have trouble finding all of them in stores.
Ganondorf seemed to be the most scarce amiibo out of the bunch, yet you might be able to find him elsewhere eventually, should you fail to get him in the first days.
You might also want to get Olimar first as well, even though he's somehow easier to produce than Ganondorf. The fact that he starred in a very few games didn't prevented him to be still easy to find in Europe at least.
I'm incredibly surprised that Zero Suit Samus is a bit more common than I initially thought, even moreso than Ganondorf. In Japan, she seems to be hovering around uncommon and semi-rare. If you already have Samus amiibo from Wave 1, there's no point in collecting her Zero Suit form unless you happen to love the character that much and/or being a hardcore collector.
Dr. Mario and Bowser Jr. will be relatively easy to acquire despite being a store exclusive. Heck, that exclusivity might even give you even more time to collect these guys rather than hopping from one store to another if your luck ran out. They're also relatively simple to produce and are from Super Mario franchise, so it helps them being more common. Though, I don't know if Bowser Jr. will be also up online as well. If he doesn't, I'll be forced to import him from elsewhere.