Generally, if you want to have custom scenery items, you have to make them yourself. Fortunately for you, this is a pretty simple project.
There are a number of tutorials on object making, both here and elsewhere. TJ Streak used to have a series of tutorials on object making at his site.
http://tjstreakssims.blogspot.com I don't know if this site is still active -- TJ has been gone for about five years. (He would make stuff for free, but got tired of all the carping and complaining.)
The trouble with a curved wall is the radius. These walls really have to be custom made for a particular use. If someone made you a wall, it probably would be either too big or too small. It is a process of trial and error. You make a wall, sticki it in game, and see if it fits right. If it doesn't, you go back into milkshape and adjust the size then reinstall it. This part of the process is quite time consuming.