Beno,
I believe the clips is shown in your original picture of the new wiring harness. I'm just starting my build back up after moving and renovating our house so unfortunately I've 'misplaces' the other half to the clip and only have what's left on the firewall for reference.
Thanks,
Andrew
Any chance you have a similar list of Toyota wire harness retention clips? I broke the one for the main harness today, right after it comes out of the firewall. Although, it looks like it comes on the main harness you posted, so it's possible it can't be purchased separately.