What is the best resouce for sheet metal?
Where can I find replacement sheet metal for the part that the
convertible top arms behind the seat bolt to?

 

Try fusick automotive they carry a lot of body panels

 

I don't think you will find the top attachment pieces in repro,you may have to get good used.What year is the car? ---bil

 

That part is definitely not available through the aftermarket and good used or fab your own would be your options. I think if you tried places like Desert Valley Auto Parts, Desert Dog Auto, both in AZ I believe or Memory Lane in CA they might be able to help. I'm sure there are other places people could recommend.
Brian