Not many options then I guess. M2M strap section, Gen or go leather. It actually looks pretty smart on leather. I have a black with white stitches I like to put on mine to dress it up
The BOB leather straps on Ebay look close to gen if you get a gen buckle to go with it. Some TDs such as Pure Time also have rep Breitling leather straps on their site sold separately (not sure stock on those).