Common as much is Oz with high mileage thrashed bikes, it's all to do with our wide open spaces, long distances and good beer.
Forum member GEZ635 is your man, might be able to help with repairs or new springs/rivets.
As GarnZ1R states, probably better to source another good second hand unit, but you take a big gamble and hope its in good nick, it's also cheating, nothing like a challenge and hope the fook your repairs hold up.
I've seen 3, repaired 1, still going strong but mileage will tell as I,m not sure about the weld repairs just yet.
Tig weld up all the ridges then grind out with a rotary de burr tool, you know the one that goes in a hand held drill, I can,t remember the size but can find out at a later date as I busy on night shift for a week or so.
Write down the order as hub is stripped, if it's too late, I do have the order of assemble recorded, it's critical.
This one was removed from a 73 Z1, as can be seen had been weld up and ground out at some stage and others are worn, but believe me it did not rattle and preformed as normal, it was replaced in an engine rebuild, other wise would still be on the road today.
This ones otta my Z1B, It was then tig welded up, gound out and still going fine today after about 2,000 miles.
The other has worn right through where one spring sits..