Prowler, Ebay is your friend. I picked up militay version (PSO1) with bunch of accessories and spare parts for less than 80CAD.
has them too, but that place charges a lot more. Like I said, keep looking on ebay. They pop up once in a while. Some times people sell POSP as well, that's civi version of PSO. My scope is 4x24. Works great for airsoft purposes and is compatible with Guarder side rail.