I "piece" my backs whenever I have to put in a seam anyway due to having to use 44" material for a larger quilt. I haven't found many places nearby that sell the extra wide or if they do, it doesn't match the front at all.
I could order it online, which I might end up doing in the future to get solid backs, but I have become fond of the row of piecing on the back....it kind of ties the front to the back for me.