Bought mine a while ago, so I don't have a link for the seller any more.
Quite a few listings on eBay - search for "carbon fiber strap", with "worldwide" checked. Make sure you use the American spelling - fiber. Going price seems to be about £20 now, due to the poor exchange rate.
My TAG (Targa Florio) uses a 22mm strap. Most men's watches are 20mm or 22mm. Best to measure the width "between the case lugs" to find what size you need.
Many of these speciality straps come without a buckle, so that you have to fit your own. If this is the case, you also need to measure the width of the existing strap at the buckle end, or buy a separate "butterfly" clasp from somewhere like Cousins Material House for a fiver. 22mm straps are normally 20mm at the buckle end, 20mm are normally 18mm at the buckle, although it's possible to get "straight" straps, and straps with a 4mm or 6mm taper.
If you're changing from a bracelet to a strap, you'll obviously need a new buckle or clasp.
It might also be worth buying a "spring bar tool" to avoid scratching the case when you fit the new strap. It's possible to to do it with a very small jeweller's screwdriver, but the proper tool makes the job easier and safer. They cost about a fiver on eBay.
