(NOTE: See updates at the bottom)
I have yet to see any of these for sale. Your best bet would be to buy a broken PS4 motherboard and remove it from that board to install on the board you are trying to fix.
I have a stack of broken boards (I should say "not fixable" as I can usually fix most of them) or boards that don't have the optical drive board with them so they are useless. I use these to take any parts off of that I might need.
I hope this helps.
UPDATE: I just want to put an update here to let everyone know that the links posted go to websites that are advertising these for sale, but they don't actually have any of them yet. One of them that I contacted even said that they don't even know when they will get them in. So these are still unavailable unless there is other websites that have them that I don't know about. If anyone knows of any I would love to know about it!
UPDATE 2 (12/16/2014): HDMI ports for PS4's are now available. You can get them on Ebay and other places and I also sell them.