Thanks for the reply and the link, however, they're out of stock.
Was trying to think what I could make one out of - a short suppressor with a thin overtube over it?? - couldn't find one with the outer diameter of the suppressor mentioned, only the length and the 14mm thread.
Anyway, my son got his bike out of the shed and leaned it against the fence and I glanced at it and something caught my eye!
The seat stem!
I got my vernier gauge and measured it - 31.5mm - hmmmm.
Obviously he wasn't going to let me have his seat stem, but there was another on the same size in the shed and it was black!
After confirming he didn't need it, I measured it up for length and cut it down to match the distance from the fake gas block to about 5mm past the flash hider.
It has a nice chamfer on the end as well.
Unscrewed the plastic flash hider and wrapped black insulating tape around it to match the inside diameter of the tube.
Also wrapped more tape around the outer barrel further back.
I then measured the rail and wrapped more tape around the tube to fit inside the rail.
I then fitted the flash hider inside the tube and fitted the whole lot together. No movement!
Next problem was the end of the new suppressor to finish it off.
Solution was some 30mm washers. Bolted 3 together and Heath-Robinson style, fitted it in a drill and set it going and then got out my angle grinder and ground the washers down. I then drilled the 6mm hole out to 11mm.
The suppressor was then tapped down onto one washer and then sprayed it satin black.
Fitted together again.
I'm quite pleased with the final result