Hello 300 owners.
There is a place in Oregon called Accurate Exhaust.. They will have these hangers.
I do not have there phone number .
They can be found on the inter net .. I bought a complete reproduction exhasut system for my 69 340 Dart from them , very nice kit . Complete with hangers and correct bolts etc.
Bob Hayen here in Kalispell Montana
406 752 5152 my shop number