might have found another solution https://airsoftgateway.com/collections/new-arrivals/products/scs-pistol-outer-barrel-adapter-tokyo-marui-d-o-r-broach-to-negative-14mm seems you glue/epoxy this in to the plastic barrel. £35 including shipping to UK. Can I get a tapping kit for cheaper?
Wouldn't it need to be left hand threaded bolt? seems an unpopular size as well they dart up from m10 to m12 https://www.toolstation.com/screws-fixings/nuts-bolts-washers/bolts-set-screws/c78
