RBC Flumes have the most narrow choice of end connections of any style of flume offered by Openchannelflow: flat wing walls.
The reason is simple: with plethora of end connections for all the other flumes offered by Openchannelflow there simply isn't a need for connections other than wing walls. Also, RBC Flumes are almost always used to measure the flow of water in furrows and small canals - applications that don't call for something more than the occasional wing wall.
That being said, should the need truly arise, we can certainly design other end connection types for RBC Flumes.