Good question, Do know they can run out of a specific tire. Would also ask, what do they charge to mount.
Free mounting trackside. If you run other than 180-200 rear, it is best to check ahead for availability. If you are running Michelins, it probably makes the most sense to get them at the track unless you have your own tire changer.
They offer 'free' shipping or trackside tire changes. Not one or the other, so it doesn't 'save' $ to buy trackside if u have a tire changer.