HP has the Flex IO card 3TK78AA - can it be used with G3 minis (EliteDesk and ProDesk)? In this video we use the 3TK78AA to add a second USB C port to the EliteDesk 800 G3 Mini (same steps for the ProDesk 600 G3 Mini).
FYI - the 3TK79AA is too large and will not work.
My card has L07094-001 on it - L25753 also seems to also be a popular number - the digits after the dash will vary
Links to eBay listings
This one seems to have hundreds: https://www.ebay.com/itm/225944729553...
This one calls out the ProDesk vs the EliteDesk but the card looks like the one I have: https://www.ebay.com/itm/324737931709...