These barrel end-nuts are simple to make. All you need is a set of original rocker shaft end-nuts and then carefully weld a barrel casing to the nut (see here https://pbase.com/9146gt/image/165250578), if necessary you can grind the angle at the barrel end and then drill a hole. You're almost done--the last step would be to dress the weld and re-nitrate all pieces. Not a big deal. The pin-washers are not so difficult to make also https://pbase.com/9146gt/image/165250579

The 911 RSR / 935 Rocker Shaft barrel nuts come in a set that actually has two types; a 'threaded' and 'non-threaded' version of the nut. See here