And the rail sizes will vary by bed size (you can see that in your photo) and how far the bunk needs to extend out. I also think some may be deeper than others as not all pup caps appear to have the same depth. But if you are relatively handy, you could probably make one that is a close fit to the original work.
2011 Jayco X19H (purchased 2015)
2008 Jayco 1007 PUP (purchased new, traded for the X19)
2012 Chev Traverse LT with TP