Websites like ltefix.com or routerunlock.com often carry clean copies. Be prepared to register.
Before flashing unknown firmware, try:
Unlock firmware (sometimes called "generic," "international," or "unlocked firmware") is a modified or original factory firmware that removes carrier-specific limitations. Unlike the stock locked firmware from carriers like Smart, Globe, T-Mobile, Telcel, or Airtel, an unlocked firmware:
Important: Unlocking firmware is different from entering an unlock code. You are replacing the router’s operating system, not just removing a SIM lock.