Hi rokr,
Thank you for the info on how you are using your NUCs. You might want to check out this site: http://www.intel.com/content/www/us/en/buy/inteltechnologyprovider/find_an_intel_techno.html. You can filter down to find the Intel Technology Providers in your area - give your requirements of the specific hardware revision and they should be able to track that down.
Alternatively, if it would fit your configuration, you could purchase the board-only SKU (DCP847SKE) - https://www-ssl.intel.com/content/www/us/en/motherboards/desktop-motherboards/desktop-board-dcp847ske.html, which had the onboard USB header from the start. The board-only SKU ships in 10-packs.
Regards,
Lois