If you have to use a blade style rear sight both Williams and TruGlo market patridge style blades with light gathering fiber optic inserts.
Williams calls them "Firesight." http://www.williamsgunsight.com/gunsights/image_r.htm
You'll need to be handy with tools to install yourself, as your 5R milspec doesn't have the mounting points on the barrel for open sights. I'd recommend paying a gunsmith.