I have used Lucky Gunner exclusively for my on-line supplier of ammo since the 2013 madness, when I got into this hobby. They send out e-mails a couple of times a week announcing "specials" in all the popular calibers.
Their web-site has a true real time inventory of quantity in stock. So if it shows "x' boxes available that is what they actually have. Back when supplies were tight you could place an order and then re-check the quantity and see it decremented by the amount you just ordered. Never any "out of stock" delays.