I'm not sure about the fiberglass rope on a BBQ, but have you checked out the website
https://bbqgaskets.com/
A while back I needed a rope type gasket to reseal my cabinet smoker and they didn't have what I needed on the website. So I called the number at the bottom of the page and I forget the name of the person I spoke to, but he was super nice and very knowledgeable. He was able to find exactly what I needed and get it shipped out quite quickly.
I'm posting the number here because it's on the website so I assume it won't be an issue.
631-648-3403
Good luck and I hope they are able to help you. I did see a 1.25" rope gasket on their website made out of fiberglass, so if fiberglass isn't an issue then they will definitely have you covered.