I found some on McMaster-Carr, but they only had fine thread.
I also searched Hillman (the usual supplier for the hardware store bins), and came up short there as well.
Nothing on Bolt Depot either.
FOUND THEMPhillips Hex Head
Unfortunately you need to buy them in quantities of 3000. That should last you a few eons.
Maybe you could call them and see who they supply to for retail quantity sales.
Just working on restoring my google-fu skills.