if it's for our bikes, then it is surely a DIY job, dont believe that anything even existED, even back then, let alone now.
The logic is pretty simple, separate the plate's basket from the driven gear with a neck and put a seal there to keep the oil inside.
easier said of course, time, money, a CNC mill and late is all you need....
might be worth looking into newer stuff, maybe a ducati's setup could be canibalized.
TG