+xInteresting, have not come across. Will follow this thread in case you get an answer. Ive used BigHeads for the same purpose before, but if there is a purpose made product I'd be interested in that.
Usually it's something from Bonham and Turner that's where I get most of my inserts from. But there are a few places about like clarendon specialist fasteners.
If it's just a brass knurled insert you can buy them from rs components