My mother and father always took me to Pittsburgh to see the train layouts at Gimbel's, Kaufman's and Horne's. Also, they would take me to the Penn Traffic dept. store in Johnstown to see their train layouts. Christmas, what a wonderful time of the year.
Dang Jim, ya beat me to it!! Yep the BIG THREE, Kaufman's, Joesph Horne, Gimbel's. I also think Boggs & Buhl had trains but it burned down rather spectacularly as I recall as a wee lad. Then there was Bill & Walt's Hobbies, though they did not have a layout as I recall. Dad always got Lionel through Doubleday-Hill Company, an electrical supply house that sold and repaired Lionel but had no storefront.
Still have every Lionel train and accessory I received growing up (and their pristine boxes).