You could just try waiting for it to come back in stock. Did you check local hardware stores as well as online stores? If it's out of stock everywhere, consider contacting the online store and asking them to get more stock, or the local store to get more of them. If you can't do any of those, the closest alternative is the 1600X, and if that isn't available either, the 1500X is your best bet. If no Ryzen CPU is available, try getting an i7(even an older i7 is okay, like the 2600K), and if it's too expensive, only then consider i5.
But usually if you ask them nicely some store or the other will get more stock when requested, especially if you're an old customer.