Greetings, and welcome to the forum!
You could upgrade to '0' gauge track. It comes in various radii that will accommodate your locomotives. It is no longer made by Lionel, but this company specializes in sourcing used rail and refurbishing it.
The Lionel Fastrack system also comes in various radii that your trains will be happy on.
Discover the joy of model railroading with Lionel Fast Track Layouts. Easy to use and endlessly customizable. Start building your layout today : Legac
Whichever way you go, enjoy your trains!
Larry