There are many aftermarket leather straps available on Ebay and elsewhere that will fit. A true NOS Omega Corfam strap may run you upwards of $200 and may not be worth the expense. I do prefer the straps over the bracelet though. Seems to fit the 1970s vibe better in my opinion.
Have all the straps and bracelets here for both men and women's version. Alas, not for sale as the 1970 Dynamic were my parents so keeping it all, including the red 'keys' and owner's manuals, for memory sake. You can find aftermarket straps for a few hundred online.
Omega still sells these straps, so if you want an OEM strap, contact your local Omega boutique or service center, or even try an AD. Cheers, Al