Struts thingies in the front are from a Kawasaki AR125
Control on the front handle is from a Kawasaki GPZ750 from around 83. There are two type of controls that are very much alike, if you want to go dead on accurate, you want the control that does NOT have the "Hazard" switch (you'll understand when you've seen a few controls on eBay or so. Also, very hard to find these controls with the text still present.
Foam grips can be bought on eBay that looks EXACTLY like the ones used for the SG, however, I have not managed to find the smaller type of grip used for the reloading handle (is that what it's called?)
Rear handle is a clutch handle, probably from an AR125 since the screws on the real SG are mounted in a way very similar to how the clutch handle of the AR125 looks like (and most clutch handle DON'T look like that, the screws are fitted from the top.. have a look!)
I've been studying auctions for GPZ parts and AR parts for more than two years and I have not yet seen any of the other SG parts which should also be from one of the two bike models if any... I've had a few theories (like the rod leading from rear handle to trigger being some sort of axle or camshaft) but none of them have proved to be accurate enough...
I believe several parts are scratchbuilt which renders seeking useless. If you want reference pics I can share if with you! Let me know if you know anything more
Good luck with the project!
(Are you using the monster Shoei MG42 for the project?)