Just so you are not limiting your search to 84 only.
You can apply any year C4 targa top, to any year C4 Corvette as long as the brackets on the car are from the same year range as the top.
There are 3 versions of the roof 1st design 1984 to early 1986, 2nd design late 1986 to 1988, 3rd design 1989 to 1996.
So if you get a later roof you will need to change the brackets on the car to the same design so it will fit.
Claremont Corvette has the 3rd design for sale.