Reputable Places to Buy GPM03 Battery for Dell XPS 15 9560

My battery light randomly started blinking orange last night.  I proceeded to unplug my laptop and it shut down.  I received the BIOS diagnostics message of “Battery needs to be replaced.”  I have contacted Dell support who said that the GPM03 battery is not in stock.  Where is a reputable website from which I can buy a safe, long-lasting GPM03?  Thanks!