Replacement header/h pipe flange studs?

[93 teal terror]

Anyone know where I can find some replacement ones. I believe they are 7/16 diameter and the only ones I can find are all 3/8" I tried napa, advance and autozone

 

[Vinnietbird]

I bought some grade 8 fasteners and and washers and bolted it all together.No issues for 3 years.