Arri WRC-4 to Cine RT High-Bright LED Display
This bracket screws onto the back of the CineRT High-Bright LED Display unit using the existing 4 screws
It fixes onto the top of the WCU-4 unit using two M4 x 10mm screws (not supplied).
Available in 7 colours
In the UK, I have found Westfield Fasteners a good reliable source for nuts and bolts and the link above is to their site.