I have worked on a few of these in my past. You probably know that to disassemble these units without a keeper ring will cause rapid demagnitization rendering the hub almost useless. I use to have one of those keeper rings but not sure I have it any longer.
It seems you are beyond that step and now need to re-magnitize the assembly. As I recall SA had a unit to do this and there were several home made units to accomplish the same. Your trick is to find someone who might still have one.
The link below addresses this issue and makes some recommendations. Also, I do know a bike shop in Philadelphia that features English bikes and use to or maybe still does sponsor an English bike only swap meet where all sorts of unusual things like this show up. They also have many parts for these bikes. I believe the name of the shop is Trophy Bikes. You may also want to check with our own Via Bikes in Philly as he is bound to have anything and everything also.
Elizabeth, NJ USA