As much as I loathe dealing with them Jack Max bring in a line of reasonable aftermarket magnetos.
I get them direct from their supplier but I have to buy them in $ 5000 orders which is probably a bit steep for you.
There is a ebay vendor in Pendle Hill NSW who also brings in the same line and is a lot more user friendly than Jack Max .
I don't know what inventory he has on hand , I just use his site occasiionally to price my parts that Camden Mowers do not list .
Jack Max have a web sit & I think now an on line store .
If not then they do list dealers but most would not have the coil in stock & have to order them in for you .
If you are in Victoria Jonno & Jonno (?) or some thing like that also keep the same sock & they sell both on evilpay & direct web shop .