John,
A great source is from a small company called Red Lion Train Depot. I purchased highway lines etc from them at York a few years ago. They have a facebook page with contact info and photos of their products. They are also on Ebay-search for their name or 1/48 highway lines and their products will show up. I purchased the highway lines in a roll and then just cut to the length I needed. It is peel and stick and the lines are available in both yellow and white depending on what time frame you model. They also have other pavement markings such as SLOW or STOP and also parking lot lines. I added a couple of photos of my module used for our club displays. Shows a couple of their products I used-sorry for the dark photos-my flash quit working.
Nick