The mono-shock for the Honda NT650 Hawk GT has part number 52400-MN8-671.
The mono-shocks for the Bros's and Hawk's are very similar.
The damper in these shocks is not repairable. The dimensions for the Hawk's mono-shock are:
Centre of top hole to centre of bottom hole: 306mm approx)
Diameter of top hole: 12.2mm
Length of top hole: 24.5mm
Diameter of bottom hole: 10.1mm
Length of bottom hole: 39mm
The top hole has a rubber bushing but no bearing.
The bottom hole rotates on a needle bearing.