Unfortunately there isn't any good reps of this strap. Seems that genuine strap is your answer. Look up on eBay. I have seen mostly going for 120-150 USD range. If you have connection with an AD, they can get it for you too. Please state that you need the buckle too as Omega sells this separately.
if you're looking for rep strap, if trusted dealers no longer carry them you can find them on the 'bay or ioffer. not very high quality like taka said though.