I am sure I have seen something on the interweb where a chap did the metal frame conversion. Also I believe there is an airsoft fake silencer that can be adapted, and there are some people who make adaptors (try the well-known auction site) for proper airgun silencers. And some kind of hooky scope mount that fits behind the barrel nut (mirroring a real item sold in the US by B-Square in the 80s).

The cheap crappy plastic grips seem to me rather similar to the cheap crappy plastic grips on the real thing.

Ever the contrarian, I'd have preferred it if they'd made a replica of either the full-size gun, or the ludicrous but amusing Micro-Uzi. Either of which conversions I guess would be achievable as a project, if one had the time, money and skills, by mixing airsoft parts from replicas of those two with the airgun bits of the Swiss Arms "Protector".