Will I be able to get the iPhone 6 in a store in the next couple of days without preorder?

Or will they be sold out? Never payed attention to the "new phone" and how fast it sells

It all depends on the stores near you, the amount of pre-order phones they have for their customers, and how many extra phones they get in stock over and above the pre-orders. If they get 100 phones, and 90 of them are pre-orders, that leaves 10 for the folks standing in line to buy them, if you are number 20 in line after the ones spoken for are gone, you will be out of luck, along with the 9 folks in front of you.

Not before Christmas.

Well the opportunity to preorder is no longer there since the phone is now available. As far as getting one, depends on the supply & demand & if supply > demand.