Hi, Are you sure that you need a motherboard? Looking at the Ifixit guide for a motherboard replacement for the FZ-1000 it appears that the HDMI connector may be attached to the motherboard via a flex cable connection. I may be wrong but there doesn't appear to be a HDMI connector mounted on the motherboard. If you can find one it should be definitely cheaper than a motherboard.
Panasonic Lumix DMC-FZ1000 Motherboard Replacement
Found this if you have the DMC FZ-1000-4K which looks different to the one in the guide and the HDMI port is mounted on it.