Per usual you should always check out the sticky threads in this forum for a crazy huge list of awesome strap retailers out there. For this watch I would say something in brown to play off the gold would be best, though a black strap could also work. It is also a dressier style Omega so maybe an alligator or croc strap?
Here are a couple hirsch options I think would work well, of course, assuming they fit the lug width. First is the Hirsch Lucca strap in golden brown, the second a Hirsch Rivetta in brown.