Air Arms Air Arm Shroud to Threaded Adapter

My Air Arms S410 has a shroud with internal baffles at the end. The guy that wants to buy it wants a moderator... The current baffles are ok could be better with moderator.
The shroud is ~5/8" / 16mm ( 15.94mm)
What's the best way to mount a moderator? Some type of adapter? Who makes one!
Thank you.
I believe that they are available through AA as I bought one for My S510
 
Here’s the muzzle end. Plastic baffles are inserted into the shroud. The barrel is set back a good ways.
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