You obviously should obtain a Splitdorf N, NS or NS-2 magneto. I have watched a few come and go on eBay this year. I bought two good ones I keep in my shop just for spares off eBay over the past few years. Not sure any you would find would be usable. But whatever you find should go into a shop for rebuilding and hopefully could be recovered for use. Set a search on eBay and wait.
Vahan Dinihanian in Oregon (vahan237@gmail.com, who has done all my magneto work) may have one to sell or cobble one together for you. Also check with 101 service shop owner Jurgen Hecker in Germany https://www.hecker101.de/ and ask if he would source one for you.
Another idea: I have extra parts in my shop and I'm too lazy to put them up for sale. But when someone has asked in one of the FB forums, I have sold to them to help (my spares: DAV, ZEV, NS, NS-2, DVAR mags however are not for sale as these are my acquired backups so my bikes will never die). So maybe just ask online. The mag you need could be sitting idle and no needed in someone's shop.
I understand a reproduction Splitdorf NS-2 is in the works but I can't recall where I learned that. But I suspect, in time, that will happen. Look to Crazy Horse to make that happen.
I do not know what issues there would be in trying to use a Bosch ZEV, original or the copy available from Competition Distributors (and elsewhere). I do know a 45 degree mag will work OK if you replace the cam ring with a 42 degree ring with the advance arm correctly placed. I've had one custom made by a maker in Ohio Mark Shulaw (frappi@wcoil.com). The timing of the spark will be off so very little. An Indian with a 45 degree ZEV ran the Cannonball and placed first in its class.
