You might be interested in my recent thread on Bosch part numbers for distributor caps.
https://www.volvoforums.org.uk/showthread.php?t=324380
The key point from this is that the part under the shroud is identical between the Volvo and the Porsche variants but the latter can sometimes be found cheaper. You must use the Volvo rotor arm.
The genuine Volvo distributor caps are apparently coated in lacquer to improve performance, I forget how.
I have never had a problem ordering from abroad. I have used USA and Germany frequently for car parts (and other items) and occasionally Australia and (yuck!) China. You have to factor in courier charges and UK VAT. In theory you should not have to pay purchase taxes the remote end, but this bit can be a minefield.
There does seem to be a dearth of Bougicord leads out there. The set you need is 6431.