Classicbilliards has some but it looks like it fits l55 rubber looking at the photo.
Here's a link http://www.classicbilliards.net/html/AntiquePoolTablePartsProducts.cfm?img=rubber_cusions.jpg&item=01-G17772-72&price=$115&shipping=$20&Desc=L77%20style%20Step%20Cushion,%20set%20of%20three%2072inch%20length
I know of an old bar in elk grove the guy has 3-4 sets when I get down there I will look at them to see what they fit I think they had a mueller price or inventory tag on them, but I didnt see them on the website.
Craig