The sellswords front end is the Opus kit here:
The barrel needs a freak insert, and you need a donor Crossman air pistol such as this:
I can’t remember where I got that from. Check the suitable models in the Sellswords information on each kit then look around UK country sports retailers etc
In the current world climate it will take a bit longer to arrive and factor in Import VAT & customs handling on top of the bill
Watch his videos on building them. You do need to do some modifying to the airpistol, grinding down a catch etc and it’s very easy to think you’ve done enough.
I cracked my first kit being too impatient, so ended up getting another.
It’s pointless, expensiveunder powered and out gunned.
It’s a stupid idea
But it’s awesome