The Volvo PN for the shoulder stud is 1328034 but a search for that didn't turn up anything readily available.
There is a VW rocker cover stud on Brickwerks but I'm not sure it is correct:
https://brickwerks.co.uk/product/stu...2-0-aircooled/
Like v8Volvo said the best bet might be a breakers but it would be good to know the dimensions of a complete stud before searching.