If you call and order for an August hatch, you would probably see more chicks from more breeds available, but your chicks would not get to you until after they hatch in August. If you got to Mypetchicken.com and click on the various breeds, select for gender or straight run, the tables shown there will indicate on what hatch dates are still open for ordering or if they are unavailable.
Different hatcheries, of course, will have different breeds available. And sometimes, the closer the hatch date is, customers cancel orders, and those breeds then become available. So there's a chance you might be able to get chicks that you desire much sooner than you think. It's a matter of stalking the hatchery wen sites until you find what you want when you want it.
Then it becomes a waiting game and it's stressful to wait to see if your chicks have survived the stressful trip through the mail, often arriving very thirsty and cold after being banged around for an average of 48 hours.
Even if you go buy chicks from a feed store, those chicks have been subjected to the same shipping process to get to the feed store, but the dead and sick chicks have already been weeded out of the shipment when you come in to the store to select your purchase. That doesn't guarantee you won't get home and find you have a sick chick, but it's a little less likely.