Yes,there are hardtops made for the 350Z roadster.
Do a search online. I believe Seibon made one in carbon fiber for around $2,500.
Smooth Line also did one for about 2k +finish options.
Only problem you may have is availability.Since these tops were made quite awhile ago,I
do not believe there will be many sitting in a warehouse ready to be delivered.
But,you never know.You may find one on ebay at a discounted price.
If it were me,I'd do the CF Seibon.