I’m trying to buy one and I ordered one from live aquaria but got an email saying it can’t be shipped right now due to species availability even though it said in stock.
They're simply listing stocking based on information they receive from QM (or any other suppliers). If stock changes at QM's end, they can't change that and did good by updating you.
Op, in case you didn't know, Live Aquaria never touches a fish. They ship directly from Quality Marine, a wholesaler, as andrewey said. If QM messes up a count or doesn't update their inventory there's nothing LA can do but inform you which they did. I've had it happen a few times with LA. DD does take possession of fish.