Well i hope it's ok to post it here, if not, please forgive me for this
This sling is till a work in progress, the way it is now is quite comfortable to wear on my right side with a single point sling.
What you will need to make a p90 sling mount:
~40cm (~16 inches) of 25mm (1 inch) wide nylon webbing
~65cm (~26 inches) of 30mm (~1.2 inch) wide nylon webbing (you can also use 25mm here if you want)
~10cm (~4 inches) of 25mm (1 inch) wide velcro
1 x 25mm metal rectangle
1 x 30mm buckle (this depends on what ling are you going to attach, i use a 30mm wide single point sling