At most toy stores or online
Where Can I Find Wall Stickers That Look Like Train Tracks?
You can go to the stationary and ask them to make one especially for you, if they refused, then ask them from where to get one.
There are websites (like fathead.com) where you can create wall stickers>
Amazon - eyecandy wall art makes curved ones and straight ones to place on the wall - just bought them for my son's train room
You can go to www.TradingPhrases.com and on the custom quote site ask them to make one.