Some on eBay. If you're taking all the roll hoop and trim out from behind seats that'll be all the fasteners gone. TBH they're a right faff, very stiff - never used mine!
Simples!
I always leave mine open inside, makes it very easy to fit and it does look good. I have never yet come across broken fasteners.
Normally plenty on eBay but expect £100>£135.