Where to find vintage correct 1/2" front leaf spring bolts?

[John Wymore]

I have a 70 Dart Swinger with 1/2" forward leaf spring bolts. Does anybody have a source for vintage correct bolts in 1/2". The 5/8" ones are readily available but I can't find 1/2". The closest I have found is a Grade 8 black oxide spring bolt from American Spring.

 

[Moparparts]

I have some nice original used ones PM me if interested