You can try using the make Oval tool to create an arc. In vertex mode delete the side of the oval you do not need. Extrude the remaining surfaces to give the arc some dimension.
If you do not need the flat side of the remaining arc, then switch to surface mode and select the flat surface and delete. Delete any other surfaces you don't need in this fashion as well.
You can now manipulate each vertex to fit whatever you want the arc to fit.
This is not as "easy" as the arc tool in Cad. But this should work.
