What is the official name for these jumper wires?

Dupont is a manufacturer of plastic products, much like Tyvek or Molex. The name has become synonymous with 0.1" 2.57mm headers, especially with jumper cables like these. As far as I can tell Dupont doesn't make these headers themselves.

This is similar to Molex being used to refer to computer 4 pin power connectors used for 3.5" drives, just because Molex does manufacturer them.

The real name of any part is whatever the community has de facto decided to call them. The real technical name is 0.1" Square Header on 22 awg Breakaway Ribbon Cable (with male to male or male to female or female to female or whatever as appropriate).

On EBAY, it is "40-wire male to male Dupont Ribbon Cable" or some variation of these words. For better hits on EBAY, search for "DuPont Ribbon Male -Female", where the "-female" excludes all matches with the word female, otherwise it would include male-to-female and female-to-female cables.