have accidentally broken the F_USB1 (USB 2.0/1.1 Header) cable. This appears to be a Gigabyte only cable that I cannot find online
usually you can find links to any available accessories either through the motherboard manual or it's manufacturer product support page(s).
but i've had similar issues with other manufacturer's accessory products not being available, even through their online stores.
if this proprietary USB splitter isn't offered through Gigabyte directly and not available on Amazon or eBay
you may just be out of luck.
start a support ticket through gigabyte and hopefully they will either offer to send a replacement or connect you to a direct buy option.
it's possible you could find a USB 3.2 > 2.0 adapter, but i'd hate to give up any 3.2 headers.
worse case scenario; return the board or file for RMA
and just be more careful with the new cable.