you are looking for M10 outer thread and M6 inner thread bushes. You might be able to get these direct from matchbox or Drennan but at a cost.
Maybe find yourself a friendly engineer who might turn you a few up.
Or buy some M10 outer threaded tube that is either already M6 inner threaded or get it tapped out and cut to lengths and use an M10 nut with thread lock at each side. The nuts would need to be low profile.
Personally I don’t care for the matchbox fastners as they eventually come adrift with constant use.
I’m sure there will be some once a month matchboc fan that will tell me different.~clap
BEST OF LUCK finding someone in the UK to supply you onesy twoesy at a reasonable price.