I got one of the items that I need at least of them all. The GoPro Hero plug that I ordered through Tindie (https://tindie.com/shops/kineteka/gopro-hero-30-pin-male-connector/).
And it is small. Really small. Tiny pins to soldering. And I haven’t been soldering anything the last 16 years. So this will be a big challenge for me to make a cabel out of this tiny plug.
It seems much bigger on the picture.
Here’s some photos from Tindie: