For the headset try chefscreations.uk
http://www.chefscreations.co.uk/portfol ... /ir-sight/Not sure what the lead time is but he may be the only 'active' maker of headsets at the moment. There are couple kits that come and go from various people on the secondary market.
Regarding the smart gun, keep in mind that maker's kits seldom come as clean as they appear online. With some elbow grease you should be able to make them work, but be aware it is a labor intensive kit primarily requiring a LOT of cleanup from the sloppy foundation. You can get a far more accurate and clean kit from
https://matsucorp.com/ , but you may end up waiting years for it. I am not sure how his current back-log of work is going. The quality is top notch, but you do have to pay a premium and wait a VERY long time. Personally I recommend building your own off an airsoft MG42 (assuming you can source one). More fun, more accurate than the golden armour and had much faster (and possibly cheaper? if you know how to hunt) than a Matsuo. That wouldnt be very light-weight though.
For the plate, try 'pepekura' to build your own. Not sure who makes accurate plates anymore.